#geometry-and-trigonometry
1 messages · Page 12 of 1
yep
it should be 7.07 (rounded off) afaik
no, PQ'
Oh my bad
yea u r right
I meant the RQ' and PQ' will be equal
whatever it will be cos45 = PQ'/10 {PR = 10}
it's also a 45-45-90 case, so 7.01 *square root = hypotenuse = ~10
then u can find the value of RQ' using Pythagorean theorem where RQ' = hypotenuse^2 - base^2
having the value of PQ' u can get the value of QQ' & RQ' ..and with these u can get the value of RQ
thus, leading us to using pythagorean theorem once more to finally find RQ, or the hypotenuse of te right triangle RQQ'
Yea that's it @gilded lion
I hope u get it
that's actually a pretty cool way, balls stealer, i only realized that now
but if ever u'd like the easier way @gilded lion, u can refer to this
indeed!
another way i found to find PQ' is through the equation 10^2 = x^2 + x^2
as PQ'=RQ'
It did thank you!
Idk the answer...of my problem
Actually i did it guys
hi.. guys?
ok i have some formula
Inverse trigonometric functions and finding the angle of a right rectangle (as long as with sine): θ = arcsin(a\b)
you only know the length of that diagonal line and nothing else?
I will try to solve it in the chat
whats the problem?
for me - no
I'm confused
ok
no, I don't get what you were trying to say
something smart
a, b its 2*(a+b) =
h*2
who are you talking to now=-=
with myself so that I understand to myself that I said something reasonable, and not necessarily correct
question?
?
ok i'm just talking to you through a translator
ah, its confusing to talk to you, I do not have a mathematical problem only here to help
ok
example of this:
θ = arcsin(a\b)
a^2+b^2=h^2
15^2+20^2=150^2=300
θ = arcsin(15\20)
θ = arcsin 0.75 \ n2
0.75\3.14*2
≈ 0.47
θ ≈ 0.47
I finished everything
can you please take a picture with zoomed in
the angle subtended by an arc at the centre is double the angle subtended by it at any point on the remaining part of the circle
and arc EB (4x) is subtended by EDB here
see the arc of length 4x between E and B
yes
we say that, the arc is made or subtended by EDB
actually there is a theorem that if EAB subtends an arc of length say x, D being anywhere on the circle will subtend the same arc with angle EDB = x/2
incase I am just confusing you more, check this out,
This is a graphic, simple and memorable way to remember the difference from a chord or a tangent or a segments and sectors! I made this after struggling to understand it myself, once i got to grips with it i decided to help others who were also stuck.. so this video was created...
This video includes Perpendicular bisectors of any chord
the ang...
its a ninth grade concept
ok thanks
thanks for letting me know...
are you calc student
no im taking pre calc but my friend asked for geometry help
oh
you will just practice
i can feel the pain
It's not a diagonal...
it isn't a diagonal but it is a line which isn't horizontal and also not verticle but diagonal
With?
what exactly
(ABC) is for the circumcircle of ABC right?
Yes, the circle that passes through those 3 points
Is there a name for the group of shapes with n foci? (like created with n pins and a string)
For my working out here
Is the line supposed to be going through the circle at two points or is it a tangent?
Cause I don’t think this method works if it goes through two points? As the radius isn’t equal to the distance between the centre and the line then
that is correct
the lines when k = 0 or k = 15/8 are tangents to the circle but if k<0 or k>15/8 the line goes through two points on the circle
If you are trying to draw the line where k=15/8 then yes it would be
As in y=15x/8
If you just drew a random line then no it would not be a tangent since it does cross the circle at two points (very close though)
Ye ok then
Ye I just saw the question mentioned two distinct points
Are u taking further maths right now
Yes
What topic are you guys on
I mean we are doing 4 different topics (4 teachers) rn: Linear transformations (with matrices), Trigonometry and modelling, Functions and graphs and distributions
Although we jump all over the place
Like we do the last chapter in the text book before the second
Year 12 currently
So a lot of the stuff I am doing rn is just normal maths year 13
I see
I’ve done most of the second year normal maths and further maths
But I skipped over matrices with transformations first year
Yeah they love skipping random things
Wasnt something I could self teach myself for some reason
Most of the maths I learn I can’t even apply to normal maths questions
Our teacher is making us to discrete and no one wants to do it
If u use complex analysis and calculate the mass of the sun I think it’s 55
Na it’s actually 1 solar mass
Mortifying
Sleep schedule is in the gutter
Although that goes for all further maths students
Not really
Chemistry takes up more time
And it’s like not difficult to pick up the further maths concepts
I wanted to do a past AS paper for normal maths and use further maths for all the questions and this and a binominal expansion was the only question I could actually try to do so
Cause u can use maclaurin series for binominal expansion
I have heard things about chemistry…
I do Maths, Further maths, Physics and Computer science
So I do not know the horrors of chemistry that I have been told about
I would answer but I do not know what the maclaurin series is
So I got a big question about solving a triangle
Say I need to solve this triangle. So the first obvious step is using the law of cosines to find the missing side. Afterwards, I would use law of sines to find the angles.
So rounding up my numbers, I would get that a=11.1
I have like three questions about finding the measure of the missing angles.
- Should I use law of sines to find the missing angles or the law of cosines?
- If I use the law of sines, say I want to find first angle B so that would be B=62.4°, but if I also consider the supplement I would have B=117.6°. And so I gather that there are two solutions. However, if I first find angle C, then I would get that C=79.6° and if I get the supplement I would get C=100.4°. So is it correct to say that there are four possible triangles?
- Should I use the law of cosines instead? Or should I valid the law of cosines for the four solutions I got and then discard the ones where the law of cosines does not hold?
in this case it is preferable to use the law of cosines because there are no risk for ambiguity of which angle is correct
there is only 1 possible triangle; the reason that sine rule produces extra possibilities it because you are putting in two sides and a non-included angle (SSA), while for cosine rule you are putting in three sides (SSS)
here SSS implies congruence; SSA does not
Like u would make f(x) the thing your expanding then evaluate it at f(0) for the first term then find f prime(x) and evaluate it to 0 and get the second term and for the rest of the terms u do the same but divide the f(0) by 2 factorial the 3 then 4..
ed1r0n
could u elaborate on this?
Segment ED intersects the two sides of triangle ABC and is parallel to the side AB of triangle ABC, hence ABC and triangle EDC are similar, and the ratio of their corresponding sides and angles are in proportion
basic proportionality theorem, or think of the triangle ABC as a version of triangle EDC scaled-up proportionally
EDC = 180-4x (angles on straight line sum to 180)
2x + (180-4x) + 78 = 180 (angles in a triangle sun to 180)
Then solve for x
And then because the two triangles are similar the angle y = the angle 2x
y=2x
Solve for y
yeah this was my equation as well.. just got skeptic of x from this coz the measure of the 3rd interior angle of triangle EDC is quite not the way presented in the diagram
True since you would get 24 degrees for it but the diagrams are sometimes very not to scale
And I don’t see anything wrong with what I have done
i guess so.. but from the equation, then the triangles are isosceles
seems like it
I do see where you are coming from but I am going to say the diagram is very not to scale
Since the maths we have done seems to be correct
wdym by where i am coming from? 😅
Means that I understand why you would be skeptical about the value calculated for x
ahh ok
Why would it be preferable to use the law of cosines? I guess that if I used the law of sines, I would need to use the law of cosines to confirm my result?
You're given an angle between two sides
All 3 of which is given
Have you read my entire message🤨
Yes, I did. I still understand that law of sines is viable. If I know the concept correctly, congruence has to do when two triangles are exactly the same, so I don’t get that part
If you use the law of sines it is not immediately clear whether the desired angle is acute or obtuse
You are given two sides and an included angle, so there is only one possible triangle (because SAS implies congruence))
Just to ask again about congruence. Which two triangles would be congruent? Or is there a second meaning for congruence?
need a hint (like where to look at)
Urm for me I would just look at the nine point circle but that maybe a circular proof as you probably get the 9 point circle from this
My hint would be to try to prove BHC and BXC are congruent
oh i had done it and tried to use it to proof that ABXC is a cylic quadrilateral
but i wasnt sure if that is enough
Oh you did it the wrong way, do you know reverse construction?
Wait actually you dont need it
Dont worry
Urm so BHC and BXC are congruent immediately by the fact that X is the reflection of H over BC
Then you just need to prove angle BCX= angle BAX,
oh
Which is obvious by angle chasing
ah dont forget that lol, cyclic quads are important especially if ur looking at egmo
trying to not forget it but im having a hard time remembering it
i often do it wrong
but ty
Ah no problem
The linear scale factor (for each line) is 9/8
So the area scale factor is (9/8)^2
=81/64
So 81/64 x 320 should get you the answer for a)
Then for b) 24 x 9/8
Then for c)
Get the volume scale factor: (9/8)^3
729/512
So 1536 x 729/512 should get you the answer
This good?
yeah thank you very much
np
Hi everybody, I think I found a proof for the area of a triangle without having to know the height of the triangle
For a isosceles triangle:
and for a equilateral triangle:
heron's formula? :)
oh
sad life
i thought i was genius
Idk if it's simpler tho
my formula is shorter right?
is there a proof for herons equation?
never hurts to feel like. :)
ofc, it's ancient
oh well, it's based on two circles with the radius of the sides look:
then u just use this formula for the two circles
and then you get a solution for where the two circles come together
then u get your coordinates
thus the height
then use h*b/2
and then you have your area
also, the height is this
you get it?
wait lemme read
oh alright
oh, that
so you basically constructed a triangle, yeah
kinda clever, but I'd just solve an equivalent system of eq. lol
yeah, i get it, so you don't think it wouldn't be useful for mathematicians?
heron's formula. :)
also height = sqrt((c - (a^2 + b^2 + c^2)/2b)(c + (a^2 + b^2 + c^2)/2b)), may make it look simpler
yeah, i agree
sqrt((cb - (a^2 + b^2 + c^2)/2)(cb + (a^2 + b^2 + c^2)/2))/2 = A
any quadrilateral?
15
correct how tf
you usually study those in 9th grade in my country, and I've just extrapolated it, so 15
i know, but im in 12th grade tho 😂
also you're usually interested in that at 15 years old
also my grade system is different
not that different for sure, but still
you jumped a few classes, didn't you?
haha ye, 3 to be exact
lmao
interesting how you considered it something valuable. I also would for a second ngl, but it would just not make sense if there was no such formula alr
@flint wagon you can look up a geometric proof of Heron's formula and Brahmagupta's formula respectively, as they exist. they are beautiful in their sort
yes it's true, mathematics has been in existence for a while, so someone must've considered finding a formula for this, which indeed happened to heron
I'll do that
ayo @pliant roost check this out
this does't happen with my formula
so maybe mine is kinda better?
no, it's exact
just computation may bring issues
which is fair
but your formula will happen to do the same :(
oh, why?
because that's how computation works
I am not a numerical stability expert
but the deviance grows, as one side tends to s, and other to 0
so the value jumps around
oh ok
but, i'm wondering, what would happen if you'd equate the two formulas to each other (mine and heron's)
try it
can someone show me how to start
could u elaborate?
You can say that assuming that sides ST and QR are parallel.
Which I can't find as an explicitly mentioned property in the question.
lmao
that's why everyone subs s for semi-perimeter lol
it's just easier to remember
true
PT = PR + 2.4
PR = x
PT = x + 2.4
and if you are confused about the 3ST = 4QR
then lets say at 3 ST is 36 then 1 ST = 12 (it doesnt really matter what number it is as long as the ratio is the same, but i would suggest to use numbers that can be devided easily(you know or memorize))
if 3ST is 36 and 3ST=4QR then
QR = 36/4
QR = 9
Then you can
12/9 = x+2.4/ x to find the answer
Hello! Isosceles triangles have 2 congruent angles. I found a proof for it. Is it correct?
why not 36 instead in the ratio of 12/9? coz I thought 36 would be substituted to 3ST
Looks convincing enough.
oh wait im kinda getting it now
coz if it were 36=9 then ig this isn't equal
Ok, thank you!
Euclid's proof of the same claim is rather more complicated than this; the commentary at http://aleph0.clarku.edu/~djoyce/elements/bookI/propI5.html suggests some reasons that might be.
See also https://en.wikipedia.org/wiki/Pons_asinorum for more discussion.
Yeah, I saw it already. But Euclid's proof looks a bit too complicated. If the proof I sent is right, it's much easier to understand and memorize
Yeah, it's what both of the sources credit to Pappus.
There has been much speculation and debate as to why Euclid added the second conclusion to the theorem, given that it makes the proof more complicated.
the second conclusion sounded reasonable tho
Nobody disputes the second conclusion is true, as far as I understand.
were the auxiliary lines of the same distance from the base?
Yes.
Hi
So there is this funny thing that is called "volume of partial cone/triangle" and well i want to learn it, but i do not know where to learn it.
Do any of you have some sort of website for learning and doing exercises?
i only need to understand what (as L is on the angle bisector) means?
i dont understand the sentence/wording
i understand the rest
but what is meant by "as L is on the angle bisector"
is it just like: L is on the ray AI which is the angle bisector of angle BAC
Yes, plus the central angle theorem for the arcs BL and LC, which says that AL also bisects angle BAC.
is central angle theorem just inscribed angle theorem but the other way around?
oh wait
Yes, that's another name for the same theorem.
ah ok
thank you ❤️
Taco
I'm pretty sure 2 and 3 are wrong
And then like all of the 2nd page is probably wrong
am i on the right track for these two
is it possible to rewrite the function y=xsin(x^2) + 1 in terms of y? (solving for x)
Not in general -- the function isn't even injective, and y=1 could lead to x=±sqrt(n·pi) for any natural n.
Even restricted to small intervals where the function is injective, it looks too cursed to be likely to have an inverse with a nice closed formula.
How? I dont have that knowledge
triangle BCO is isosceles, triangle ACD is right.
Ohhj right, because of the radius
Also, how do you know that triangle ACD is right?
multiple ways to show that
for example from the fact that triangles AOC and COD are both isosceles
and so angle OAC + angle DOC make up exactly half the total of internal angles in triangle ACD
But if the angle OBC is 32° and triangle BOC is isosceles, then the angle OCB is equal to 32°, triangle OCD is also isosceles so the angle OCD is 67°, 67 + 32 is 99°
That's the ACD angle
Which would mean that triangle ACD is not right
angle OCB + angle OCD is not angle ACD
it's angle BCD
which need not be right
in fact it differs from the right angle ACD by none other than the very same alpha you seek
Ok I see it now, thank you
ty
well to understnad trig well u need to have a basic knowledge of geometry
Geometry isn't hard
Tip: If u wanna master trig right now, the geometry of triangles is crucial
I think geometry can be pretty hard. I skipped to trig too, now in calculus and there’s a lot of problem solving that has geometry related stuff, it’s hard if you didn’t do geometry haha. Trig is easier imo but ofcourse you need very basic geometry understanding for trig.
Honestly geometry requires alot of critical thinking I guess?
Like even just using all the concepts you've learned could be pretty hard
The geometry that’s taught in schools require memorization. But on the SAT math section, that requires critical thinking
that is a lot of problems.
Those problems really test your memorization
Hello! As I know, every triangle can be divided into 2 right triangles. Should I prove this statement, or it is too obvious?
You can say something like "We draw an altitude to the side AB which divides the triangle into two right triangles"
Nothing really to prove...
I thought it needs a proof because if you have an obtuse triangle you can draw an internal perpendicular not to every edge
Every triangle must have at least one angle which is either right angled, or obtuse. If it's obtuse, you should make the base of the triangle be the side opposite the obtuse angle, and then you can draw an altitude down, as you've shown above. For right-angled triangles, it's a special case where you can make two smaller similar triangles
Hopefully that kind of makes sense in words
Oh wait shoot take that back
Yeah, I understand. But how do I explain it? Is it an axiom or what?
I wouldn't say it's an axiom, but definitely quite a common fact. If you wanted to prove it, you can probably continue to think about the properties of triangles, and their internal angles
Only flaw in this argument is if it's an acute triangle, but that should be obvious from a sketch
If I am writing a proof, can I use this "fact" without proving it?
Depends how rigorous you want to be in your proof. If it's a relatively rigorous proof, then probably start from scratch and prove the fact before using it.
Although, I think most people just use the fact as a given, so you should be alright if you wanted to just use it
You can always draw an altitude to the longest side of any triangle
Ok, thank you!
You can construct the point the altitude will go to using the pythaogrean theorem which is a proper proof
Using the formula and lengths of sides?
Yeah
I will try, thanks
np
I tried. It helps to find the point where perpendicular touches the edge, but how does it prove that any triangle has such point?
you have a point so you proved it exists lol
now you need to show that it is positive
What exactly?
And if it's not? Should I just try another edge?
yes
it is guaranteed to work if the edge is longest side
so use that hypothesis
Ok, it makes sense. Thank you
Yeah I was more talking about the SAT sections or math olympiads
Have you taken the SAT
Nope, but I have seen some papers. It's not really as prevalent here as it is in US
Where I live it's mostly just olympiads or competitions
Using my previous formula for c2 and c1, I tried to prove that if c is the longest side in triangle, c1 and c2 will be positive. Is it right?
If I solve a trig quiestion like 7tan30 how do I make it radical form, pls help
tan(30) = sin(30)/cos(30)
i know what 7tan(30) is as a decimal, how do you find radical
I love trig and geo.
can you help?
so to find 7tan30 you just put in a calc but the calc at school only gives decimal form, 4.04145188433
how do i keep in simplified radical
firstly tan 30 = $((1/2)/(√3)/2)$
Ishigami Senku
therefore: tan 30 = $1/√3$
Ishigami Senku
then multiply by 7 and you get $7/√3$
Ishigami Senku
the calc only gives decimal number how did you get that radical
I learnt surds ⚔
and .....
Just send a DM and I'll explain
further.
when you guys have to solve a geometry problem which is like this, do you draw the figure on a paper or are you able to "see" the figure
idk how to describe it
but, do you just see how the stuff is going to look like?
Always draw lol, Geogebra is a good app if you need it,
could be coz of the 30-60-90 triangle case, where the length of the longer side is (n) sqrt3 times the length of shortest side (n), and the longest side (hypotenuse, n) is twice the length of the shortest side (n)
damn me too 🤝
If I knew theta (written in black), does that mean I know theta (written in red)?
i believe so
Only if the lines are parallel
pls name the points of the triangle so it would be easy to describe
call top point a and bottom right b
yeah
they are parrellel, but obviously mc is longer. does that matter?
no it doesnt
thank you so much
my pleasure
In general, if 2 parallel lines are joined by another line, then the angle made by the line joining the parallel lines will be equal
I'll send a figure later
yep, hence, <E & <C are corresponding angles
Here is the actual full question and my working out. I can't see anything i did wrong but the numbers seem a bit off. Can you check?
final answer looks correct to me.
For most of those you should try taking a term to the right side
That should provide some clarity
for example write sin2x - sinx = 0 as sin2x = sinx
You know that sinx = cos(90-x) right?
The 2nd one is a bit of a tricky one.
When do sine and cosine have opposite signs?
when they are in the second and fourth quadrant
Yep, so your answers lie there
I'm not really sure how you'd go about showing your work
ahhh i think i kinda get it now
You could also use the formulae for sin2x and sin3x if you want
Yeah you can do like 2 of those with complimentary angles, and the rest with the addition formulae
I’m not 100% sure on part b
But I got 7.67
I find the equation of the line passing through The centre that is partake to other line
Then I found the equation of the normal to that that goes through circle
And find where it intersected the circle
Then found the distance between that point and point where the line given crosses x axis but idk if this is right cause it seems very long winded
@edgy panther Hey I found out how you could go about showing your work for the 2nd one
I didn't notice the sin(-x) and was confused the entire time
But you can write -cosx as sin(90+x)
@violet shadow Did you find the coordinates of the centre?
Ye that’s 5,4
I guess you could go about finding the perpendicular distance between l and centre then
I don't really understand what you meant so you might have done this only
Lol
Ye but it wants shortest distance isnt that from the edge of the circle?
First try the shortest distance from the centre, then subtract radius ig
It seems right for some reason
Shortest distance between the centre of the circle and the line is the perpendicular distance from the line
Idk if that’s what the question wants tho
But ye I think your right
Find perpendicular distance and then subtract the radius should work
Yeah, I just can't find a good explanation for this
Maybe something to do with right triangles
I'll brb
I've got it I think
I'll send a clean ss
I got 5.497
Perpendicular distance is 19root 5 all over 5
Subtract 3 which is radius
@violet shadow
I guess this counts as a proof?
Line n is a tangent to the circle at the point where perpendicular distance cuts the circle
And it's parallel to the line l due to angles
So the distance between the parallel lines is the same throughout
And n only touches the circle at one point so that means that's the minimum distance
Well u have to find that line then
U have to find the tangent to the circle your way then
Which is long
^
Let's go, smaller than your previous answer
U got it aswell?
Ye I think my 7 was wrong cause I did it a long wounded way
I think this is correct tho
Something about shortest distance from a circle
I usually use further maths for geometry
Cause there is a formula for perpendicular distance between a point and a line
Honestly geometry is scary sometimes
You don't know if the question wants you to do it a long winded way
Like say, finding the orthocentre of a normal triangle
Oh there is?
Yeah I vaguely recall something similar
I saw a formula for perp distance from the origin nvm
K
yeee you re right now it makes sense
Can someone help
help with...?
Do you think I could of used law of sines after I found the angles?
Honestly, you didn't need to calculate tan inverse of 10 either
Then how to get the angle?
I have no clue how to do this and need a walk through
ask a help room
(answered in another server)
How would you do it?
Sorry for not responding, I was asleep at the time lol
But since you found the 2 angles to be equal, you could have simply set tantheta = tanalpha. And since the question is just asking for the diameter you don't need to calculate the angles @upper karma
help
help with...?
Okay, what would you need to write an equation for the circle
Just to clarify, equation of the circle means equation for points lying on the circle
okay, what's a speciality of circles that you can use to your advantage?
they form diameter?
or, each point lying on the circle is equidistant from the centre
radius
Though I guess you don't even need that
The question isn't asking for the equation of circle
it is
It's just asking you to find the diameter
But that's not what an equation of circle is, atleast where I've read
That's mostly just asking you to apply distance formula
wait for this??
by finding 2 points of a diameter
Distance formula is for finding the distance between 2 points
Could be used wherever convenient
Didn't you basically apply distance formula here?
for my question, we just finding the center
nope
we got the points from the graph itself
You found the radius of the circle
Alright, sorry I was confused by the wording of the question
it's alr
Been a while since I touched coordinate geometry
So yeah, these questions require you to locate the centre
Find the distance between the centre and a single point lying on the circle
and then apply distance formula for all x,y that are the same distance from the centre
-3,4
BUT SHE SAID WE AINT GOTTA USE ANY FORMULA FOR THE QUESTIONS THAT HAVE GRAPHS ON
the question is literally asking you to use a formula
You can't really not use a formula there
Let me confirm: You did this by calculating the radius, and then applying distance formula for all x and y that are the same distance away from the centre right?
Just do what you've already done
hello
i want to have a discussion about 4th spacial dimension
this word "space" is important here
because time is also known as 4th dimension but I am talking about space specifically
does anyone have an example of a 4th dimensional object or thing which exists in real life?
which can be observed?
or measured.
Don't tell time.
wait actually I get it now
tysm anyways!
no lol what
we live in a 3d world
but does that imply we can't observe or measure it?
yes
we cant even imagine it
well
a circle can cut a line
so a point in line can see those atmost two points of the circle
a sphere can cut a plane
so a 2D being can see those curves
similarly
why can't something 4D come in contact in our space?
where is it
it would be a 3d shadow
u have any example please?
yeah one sec
not necessary
and then, what if 4D doesn't exist at all?
it may not
but what if the nature of space itself is like that
such that space can only have 3 dimensions
i hope a mathematical proof or disprove in the future
why
well thats another thing
this doesn't stop us from observing it if it ever came in contact with our dimension
thats not a proof
so
so what
it was never meant to be
if we can somehow find it existing yeah
but Im saying you cant prove it with like math
hm....
itd have to be shown through experiment or smth
maybe using dark matter
who knows
many people are actively working on these kind of questions
maybe you will too one day
saying "we can't" is just as arrogant as saying "we can" I guess
it is just left there
thats why I said hope
we could mean nothing
well we already are
That is definitely wrong.. unless I’m not understanding what you mean. Have you looked at the question properly?
Allow me to explain properly
So, when you look at the 2 right triangles, they're similar
That also leads to the same conclusion that the sides are proportional
Similarly, since the angles are equal, the tan of those angles should also be equal. Therefore tantheta = tanalpha, which leads to ratio of the height from the ground to the radius of the cone formed is 10.
Even then, this question does not even require trigonometry, it's basic similarity
All I said is that if the angles are equal, then the tangent of those angles should also be equal
And that leads to the same conclusion you'd get by going the similarity route
@upper karma
Ok yeah I understand now regarding setting tan theta and tan alpha equal to each other. Thanks for explaining. How would you approach it by similarity route if you don’t mind explaining?
Alright let me name the vertices one second
So, we're considering the triangles ADE and ABC here
Angle A is common to both the triangles, theta and alpha are equal, and Angle D and B are right angles
So all 3 angles are equal
A=A
D=B
E=C
So triangle ADE~triangle ABC
Now according to CPST, AD/AB = DE/BC = AE/AC
Using this, we can say that AD/AB = DE/BC
which gives you the same equation as above
What is CPST? Yeah I never would of known how to use symmetry like that. I know basic symmetry but thats all.
Corresponding Parts of Similar Triangles
Similar figures are figures which are basically the exact same shape as each other, but differing in size
It's basically congruency but without the figures being the same size as one another
The sides of similar triangles are proportional to each other and the angles of vertices are the same (hence the same shape)
In determining similar polygons you need to see if the angles are the same
Hopefully that provides some context
A yardstick casts a shadow of 24in. at the same time an electric post cast a shadow of 20ft. 8 in. In inches, what is the height of the electric post? Let h be the height of the electric post
I had this problem recently and Im somewhat skeptical of the triangles being similar. Because the statement did not say anything regarding the angles in the triangle being congruent to one another or state that the triangles are similar. But, if you put the given measures in proportion, you'd find h. But idk how I could make the statement stating that both are similar unless I assume that the interior angles are equal or, they're both right triangles.
Imperial
@smoky jetty have you drawn a figure?
whats a inch? the rest of the world uses SI units..
lol
I know duh.. just being smartass
1ft=12in isn't it?
yeah i have, but the problem did notstate that they are similar, so I could solve it if, i assumed that both have the same angles
You have to
i have the answer, only if they are similar, but idk how I could prove that they are similar in a statement
Otherwise it's not really solvable I don't think
indeed
Okay, so it's a yardstick and an electric pole
otherwise, im having a geo concept gap, lol
Do you know much about secondary bonds im chemistry, such as van der waals?
yes, you'd get the answer if u assme they're similar, but i kinda find the given being insufficient with info
Whenever you are given pole like objects
what are your thought?
You kinda have to assume they're perpendicular to the ground
yeah i thought so as well
Unless stated otherwise
right angles baby
Yep
we love that shit
but i considered other factors being that one may be inclined as the other is perpendicular to the base
coz the problem didn't state such
I mean, we are at relatively lower levels in geometry
So I doubt the question wants us to consider those possibilities
i see
So for now, rest easy and whenever you're given poles or similar objects, just assume they're at right angles
i kinda feel bad that i have to assume their angles just to prove they're similar, lol
Yeah I know what you mean
You could also think practically, why would someone build an inclined electric pole?
do u think assuming it would prove their similarity otherwise?
lmao, i've had previousproblems before with inclined poles
Yeah but only sadists build those
lol i see
Apparently engineers are infamous in the math community
Why would they make stuff hard on themselves by making poles on slight inclinations
well ig in short, to solve the given problem, one must assume they're perpendicular or have the same interior angles?
Assume they're perpendicular for now
In later classes that might change, I don't really know
alright, thank u very much.
Eh I didn't really help
how come? lol
I just acted like those teachers who say "That's just the way it is"
ig my teacher gave that problem with that attitude, lol
Yeah, though it makes life easier for us as well
Similarity won't work always
Sometimes you'll have to use trigonometry
And in those cases the poles being perpendicular helps a lot
yeah
what grade are u in btw?
hs before senior higschool?
ig im 9th grade relative to yours
Damn, similarity in 9th grade
idk if we'll ever reach congruency&heron's, prob due to the curriculum
btw thx for the responses earlier, I thought I was the only one who had to assume the triangles were similar to solve it, or who knows
No you do need to assume them to be perpendicular
You know why the triangles are similar right
The sun will cast a shadow at the same angle for any perpendicular distance at a given time
Since angle of elevation of the Sun does not change from the ground
they must be perpendicular to the ground
yeah I thought so as well
does that need to be explicitly said in the problem?
otherwise it's just assuming both are perpendicular to the ground?
wait i messed up
You can prove the triangles to be similar by the Angle-Angle similarity criterion.
One pair of angles will be 90°.
The other pair of angles will be equal as the sun will caste light at equal angles.
You can also use trigonometry to solve this problem.
Either way proving the non-perpendicular pair of angles is necessary.
That wasn't his question though
He wanted to know why we had to assume the electric pole and yardstick to be perpendicular to the ground
yes, but the problem didn't state any given angle, so i just need to assume
It's not an assumption but more like ideal.
For eg: a tree. It can be bent but ideally we take it to be straight.
Take the angle to be ∅.
Apply tan∅ in both triangles.
Since ∅ is equal in both triangles, tan∅ is also equal.
Equate both of their values and solve for x.
Where x is height.
Or in your case it is "h"
u mean the ratio of tan ∅ in both triangles ?
i.e let's say, 36/24 = x/248 ?
Does this shape have a name, and if so what is it called?
Just a cube with a cylinder cut out from all axes.
Yes
ah yea, then you'd get x then
would u say that the problem should've explicitly said that the post and stick were perpendicular?
Um.. that's hard to answer. Mentioning it does make it more clear. So yes.
My guy, that's what an assumption is
Given the vector of coordinates v=(-3/4,k) it is requested that for k=1, express v as a linear combination of a=(2,3) and b=(5,-1)
I managed to resolve it but I don't know if it's right or if I misunderstanded the exersice
I thought v=(-3/4,k) was w and did w=x(2,3)+y(5,-1)
Break it into components
v = Ca + Db
-3/4 = C*2 + D*5
And then the y component
Two unknowns two equations
Solve
The answer is x=1/4 and y=-1/4 right?
Idk lol I didn’t solve it
Plug the values back in and check
There’s a beautiful formula for this: $(n-2)*180°$
Daniel S.
n being your total number of sides
and the result being the summation of all angles
You’re given that the polygon has a total of (x-8) sides, that’s your n value right there
So substitute that for n
and you’ll get what
@prime umbra Come back, don’t ghost me
I think they already got it
I hope so
What is your answer
pls help
Where’s the line
My bad 😓
Origami ball
Is that the Cartesian Plane? Why is there no line?
use the distance formula
$/sqrt(x2 - x1)^2 + (y2 - y1)^2$
but what do they mean by "the line"
?
$/sqrt{(x2 - x1)^2 + (y2 - y1)^2}$
Sanaltsalt
@short wyvern
yessir
backslash not forward
oof
\sqrt not /sqrt
good luck
Sanaltsalt
this is basically displacement
but this is maths
just fill in y with "the line" and you should be fine
@stray spruce
first multiply out the areas of both rectangles
Refer back to your understanding of inverse trig functions
Do you have a calculator for this
"What's the sum of all the six angles marked on the picture", how to approach this?
Is there a way to do this question part C without the discriminant because it’s very long that way
hello, can someone help me with this? just the solution would be fine.
4x-8=23
opposite sides are equal
in a parallelogram
and 47+2y-3=180
adjacent sides are supplementary in a parallelogram
A water park has hired Sharnee to build part of a ramp for a new water slide. She builds a 12-metre-long
ramp that rises to a height of 250 cm. To meet safety regulations, the ramp can only have a gradient between
0.1 and 0.25. Show that the ramp Sharnee has built is within the regulations.
can anyone show me how to do this i cannot understand
do you know what gradient means?
in this context it is also commonly known as slope, though it depends on where you are from.
yeah i know but idk how to find gradient in that question
how would you find the gradient of a line on a coordinate grid?
y2-y1/x2-x1
missing parentheses...
whats that
brackets
anyway
the phrase "rise over run" should have been said at least once in your class
yeah
She builds a 12 m long ramp that rises to a height of 250 cm.
what are the rise and run here?
find the gradient...
oh sorry
it's already answered
give it a try
Rise over Run. Rise/Run correct? And the RS/RN is the mx in y=mx+b. Correct?
I made a very rough illustration regarding the problem if u need to solve it asap, hopefully u know the nexts to do
rise over run is just the m, not mx
the problem didn't specify if it's right triangle, i hope it represented the measures correctly
Oh yeah I forgot.
I would say it would be a right triangle if the little box indicator thingy is on the straight leg.
yeah, but the problem didn't state it so
someone solve this: sinx+siny=a and cosx+cosy=a, what is sinx+cosx interms of a
if there is the square in a corner that tells you it’s a right triangle. they just didn’t list it in the problem.
i mean it's pretty hard to assume that it's a right triangle here
Help this question, find alpha in terms of a, b, c, d
Given this is a rectangle where the intersection between four lines is randomly picked
Guys can anyone explain why the unit circle is centered at (0,0)
to make life easier
law of cosines
so as not to have the coordinates of its center get in the way everywhere.
You helped lots thank you for the explanation
..?
I already finished that whole assignment
Yesterday 
10th
I’m not the best at math
u still need help?
isnt AOB 80 too?
since O is the center
and since its a circle you know 2 sides of the triangle are = so know more about the triangle
then ACB is just the whole circle missing a part, which you know
<@&286206848099549185> can anybody help with this question?
i need to find the probability of p(A|B) in order to see if probabilty of a and probability of B are independent or not. im looking to see of P(A)(B) is equal to P(A|B)
p(A)= 11/50
p(B) = 5/11
are you given more info?
yes
might be handy
the meaning of p(A) is the probability of picking cheerios
11/50 chance
p(B) is drinking the milk after eating the Cheerios
5/11 chance
just trying to see if they are independent
multiply it
is p(B) the chance of drinking milk after eating cheerios or the chance of drinking milk after eating cereal?
Its the probability of drinking the milk thats left in the bowl after eating cheerios
So thats saying the prob of drinking the milk given the fact you ate cheerios
Yes
oooh
sssno more info is given
any way to figure that out?
i meant with the probability
oh
i know p(A)(B) is 1/10
