#help-27
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How would you prove two triangles are congruent if they all of their angles are congruent?
I don't think you can, those are similar triangles
To be congruent, they also have to have an identical side
Similarity doesn’t imply congruency
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Yes
I think -rooting both sides
Then changing the greater than to less than. After that it’s important algebra I think 🤔
?!
You can't with inequalities, unless you consider each case (sqrt(x-4) is positive, sqrt(x-4) is negative, -sqrt(x+2) is positive, -sqrt(x+2) is negative)
Here's why:
-9 < 5, but if you square them:
81 < 25, which is clearly wrong
Welp looks like I’m dumb
I'd suggest the method I've been taught, but I've seen other people explaining easier ways to solve inequalities like that, so I won't
Squaring should work if we take intersections with their domain tho?
i think this ineq does not have solutions
The lhs is non negative always, and the rhs is never positive
Nice
but in this case left side is always bigger than right
right?
Yea
so we basically just solve the ineq
So there is a solution, not sure abt the squaring method tho, ive not used it in a long time
we don't have to consider both cases
Theres nothing to solve
but why
yeah but i don't understand
sqrt(x - 4) is always positive, -sqrt(x + 2) is always negative
(something positive) > (something negative)
When is this true?
Your supposed to flip the inequality
always
When u devide both sides by -square root it changes the inequality
Not exactly
but from now on idk what to do
I mean this is always true, however in this case you have to consider something else too
there's one last thing to notice, those square roots may not be always defined
so this is not true?
i'm getting confused
Follow this
Move all to left then see
if i move them to the left what do i doo after
What no😭
Consider the domain of the square roots
Let me check
Here's what going on
You know that that inequality is true, when the left and right parts are defined
You can't have undefined < something (or undefined > something of course lol)
And square roots are not defined when you take the square root of..??
Ah not working
x>=4
it does
I mean, there is a solution
We just found it
Photomath dumb

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I don’t understand how they came up with what v hat is?
Is it essentially x=cos(theta)u and y=sin(theta)u’ where both x and y are vectors
@pulsar ermine Has your question been resolved?
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Can someone explain to me why when have a numbered list with entries under numbers from 10 to 20 inclusively we have 11 entries in total? I need some explanation which explains it more logically than "just add 1"
count them on your hands?
LOGICALLY
I don't see how this is weird. if you have entries 1 to 10 (inclusive), how many entries are that in total
well imagine you start labelling the list new again
the 10th item is now number 1, the 11th item is now number 2 and so on until the 20th item is now number 11
which you can see cause you have to subtract 9 from 10 to get to 1, 9 from 11 to get to 2 and so on
you subtract 9 from every number and now the list starts at 1 and ends at 11
so it contains 11 elements
Not wanna be rude, but I asked for a logical explanation why it is so, not for a way to bring it to counting from 1
I don't have problems with calculating the correct answer, I have problem with lack of logical explanation on why I can't simply substract
I'm sorry but I can't give you a logical explanation why a list of 10 items does not have 9 items
😦
this pretty much sums it lmao
a list of 10 items must have 10 items
suppose you want to count item 2 to 4
if a list of 10 items has 9 items, itd be a list of 9 items, not 10. logically.
4 is the number of items behind the 4
you subtract 2, the number of items behind 2
the 4 itself is special, it's not counted in either
logically
i guess we can define it to include the item new picture then
now 2 gets overexluded
Let's subtract 10 from each number in your list. Now we have the list of numbers from 0 to 10. Obviously, if you count the amount of numbers from 1 to 10, that's just 10 (because you're counting like 1, 2, 3, ... to 10 up). But now you need to add 1 because of the 0
so it's like, you want to subtract the number before the 10, 20 − 9 = 11
👀
Seems more like what I would like
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Please explain to me, which ODE technique I have to use here:
Would you please tell me which?
well there should be something in your course about 1st order linear equations
or look up online
solving 1st order linear differential equations
I am sorry, but may I know which ODE technique I need to apply?
it doesnt really have a specific name
oh yeah you can do that to prove it
but for this kind of equations you can right away give the answer usually
since its always the same
That's also correct.
Thank you, mate 🙂
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Did i get my derivative right?
@bright gulch Has your question been resolved?
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and well
where does -x^3
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sin(A+B) formula
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I need help on the b) part. There should be marginal pdf of Y for cases 0 < y < 1 & y>1 but I do not understand how to find the latter.
@quartz oriole Has your question been resolved?
<@&286206848099549185> anyone who knows about conditional distributions?
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Hello
I am having issues drawing this picture in mathematica
These are my parameterizations of the lines
However, mathematica is only showing the first one
And the line doesnt start at the origin but instead of the end point of the first line at (1,1)
Why is that? how do I get it to display all the lines
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hello there
base and induction case
well isn't the denominator just n!n!?
yeah
how do you simplify
after inductive step i got
(2k+2)(2k+1)(2k)!
/
(k+1)(k!)(k+1)(k!)
idk i suck at combinatorics
Note that you want to get to 2n C n
wdym by that
yeah
oh yea
i do
i kinda see it
because theres a k!k! in denominator
Yes
Move the (2k+2)(2k+1)/(k+1)^2 out
Yes
Yes
Wait. Wouldn't it be 2(2k+1)/(k+1)?
yeah but i brought the 2 to the denominator
The left part is just 2k C k
and since the denominator > numerator that whole expression will be less than the base case
yeah
the right part of the 2k C k
is
2k+1 / (2k+2)
wdym? numerator is obviously bigger
bring the 2 down
wait
we cant do that
my bad
so how do we simplify
from here
If we apply the induction hypothesis we know that 2k C k < 3^k
So we have to show now 3^k * 2(2k+1)/(k+1) < 3^(k+1)
so we know that right
what we do from here
2(2k+1)/(k+1) < 3
That is the issue. It seems to be wrong for large k
do u think the statement is wrong
idk if thats possible tho
No, I think I made a mistake somewhere
did we mess up simplification?
Wait
I found the same question with > 3^x
can u send link'
For large enough x
The following error occured while calculating:
Error: Undefined symbol nCr
Yes, he got to this using the same method
Try n=5,6,...
His question says show for n > 5
Can you show the original question?
Yes
Yes, the factor of increase is bigger than 3 for n >= 1. But it takes until n = 5 for 2k C k to overtake 3^k
Note that for n = 5, 2k C k > 3^k
oh ok
Than do what we did
would i calculate base case from n=5?
Yes
ok thanks
And show If 2k C k > 3^k then this is true for k+1, too
Also, you can show the cases 1 to 4 per hand
It's greater for n >= 5
yeah
Anyways, I got to sleep now
kk thanks
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.reopen
,rotate
When you came to 5x+b = 22(x+d) - 17(x+c)
You assumed that x^2+3bx+80 = (x+c)(x+d) in order to do that
Yeah
Well, if that's true, that's a lot more information to work with
You have three variables b, c, and d. If you can make a system of three equations relating them, you can solve for them
You already have one.
The other two come from here
How? I can only formulate 1 = 22d - 17c
$x^2 + 3bx + 80 = x^2 + dx + cx + cd$
Jared
Yeah
So combine the like terms
And do the same thing you did to find 1=22d-17c
Equate the coefficients
Like this?
Yes. What does that tell you?
80 = cd
cd*
Yep
Real quick
Your first equation 1 = 22d-17c was not quite right
It should be b = 22d - 17c
But now with three equations and three variables
You should be able to solve the system for all three
Where do I go from here?
That's right
But maybe kind of a dead end
I'd eliminate b instead, so that your new equation is in terms of c and d
Because the remaining unused equation is only in terms of c and d
Jared
c = 67/51d
That's not exactly what I got, can I see your work?
So looks like you're multiplying by -3 on top and then adding the equations right?
Yeah
Double check. Should be -52c = -65d
wait one sec
-3(17c) -1c = -52c
-3(22d) +1d = -65d
c = 80/d
c=80/d
Substitute that for c
Wdym
$\frac{80}{d} = \frac{65d}{52}$
tatpoj
Sorry 52 not 62 lol
d could be either -8 or 8
Do I try for both?
Your goal is to find b. And the problem specifies b < 0
So yeah, try for both. See which one gives negative b
yep
Yep 👍
No problem 👍
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the question wants me to prove the height of the fountain is 34m.
ive found the radius and i have the angle of elevation, how do i find the slope?
you mean the height of the triangle you made?
just use trig
tan(theta) = opp / adj
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hi can someone give me tips for this qn pls
yo
if det(A) = 0
that means the matrix is invertible?
not invertible i mean
There’s another way of doing it I’ll show it
Yes
You can also use det(AB) = det(A)det(B)
And chosing an infertile matrix for B gives you the result
breh i cant even solve the first part
sad
what can i even get from this lol
hmm
@remote meteor yo
ill have to prove both ways right?
like, this is only one way
Oof ig
or contradiction
Contradiction is ok
A is invertible
whats thaat
And thus invertible
Ker(A) =0
havent learnt that haha
Is calculus hard?
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Obtain the differential equation that describes the following family of curves. All straight line with x-intercept at x=2.
lines are of the form y=mx+b
we know that they go through the point (2,0), so plug that in
like this y=m(2)+b?
0=m(2)+b
then the arbitrary constants are m and b?
yes, but you can find the value of one in terms of the other
is this point slope formula
yep
and m is the only AC?
i can isolate m so it would be like m=y/x-2, then differentiate?
yes
for the denominator (x-2)^2, can the equation be multiplied to the denominator for simplification?
you should get something in the form "=0", the denominator should not matter at all
okay so, y'(x-2)-y=0
then is that the final answer? it'll be y'=y/(x-2)
yes
notice that in our original equation we had:
y = m(x-2)
y/(x-2) = m
so that means:
y' = y/(x-2) = m
makes sense because it's a line doesn't it?
yeah, looks like the intercept form
now that i think about it there's an easier way to do this
we can start with:
y = m(x-2)
take the derivative:
y' = m
plug in y/(x-2) = m:
y' = y/(x-2)
ah yes, using the substitution method
btw, thanks a lot, i always have a hard time choosing the formula
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Obtain the differential equation by eliminating the arbitrary constants
y=Ae^(-3x)-Be^(2x)+Cx^3
I tried getting up to the 3rd derivative, and was thinking to use matrix but its 4 equations and, i think matrix can only be used for 3 equations
@strong hazel Has your question been resolved?
Might just want to try using the same idea with y, y’ and y’’.
Use Cramer’s rule to solve for A, B and C.
So there will be three matrix tables?
I don’t know what a matrix table is.
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hi, can someone help me with this question
@tiny rain Has your question been resolved?
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In machine learning, we use sigmoid function to setup the logistic regression.
Why we can define P(y=1|x;theta) and P(y=0|x;theta) with a pair of totally different function?
Thank you,
@short wigeon Has your question been resolved?
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Missed some notes for this and I’m confused on how to approach and solve it can someone help me any help is appreciated!
@thick reef Has your question been resolved?
Seems like you want to use bayes theorem for this
Yeah that’s the thing I’m confused on how to approach it
Or like apply it-
There we go
Start by defining some events, that way you can rewrite things using probability notation
So define an event where someone is a smoker, and another where someone dies
Then yeah, translate the probabilities into something more useable
Someone is a smoker
Probability of dying ~ 6%
Probability of not dying ~ 94%
Nonsmoker
Probability of dying ~ 1.1%
Probability of not dying ~ 98.9%
Like the probability of an event based off previous information we knows related to the event?
That's a reasonable physical interpretation
For the purpose of solving the question, do you know its formula?
No but I remember my professor using a table of some sort for a problem related to using bayes theorem
10%

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How many ways to put 13 indistinguishable balls in 4 indistinguishable boxes?
This might help
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Hello everyone! I am so confused about limits at infinity when the highest degree of numerator is greater than the highest degree of the denominator. My professor told us to always divide the variable with the highest degree to the numerator and denominator. The attached photo is the sample he kind of explained to us.
My question is, isn’t 1/0 considered undefined? How come the limit became positive infinity? Is there a theorem that mentions the limit of undefined is equal to a (or the value it approaches)?
@reef prism Has your question been resolved?
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$f_a = \frac{x-a}{|x-a|+a}$
i have to find that when we variate a all the curves pass through a point
ie $\exists x\in \mathbb{R}, \forall a \in \mathbb{R}, f_a(x) = constant$
If I understood, it’s one common point f_a(x) for all a ?
ye
Okay so you can just take two values of a, and ask for an equality
when we evaluate in 0 it doesn't work, same for a multiple of a
good idea
Like $f_{a_1}(x)=f_{a_2}(x)$
DonutsenPLS
i don't know how do solve that
Have you never done polynomial equations with absolute value ?
never
y = -x or x
-x when x <= 0 and x when x >= 0
ye i thought about it x)
So now, how about y=|x-a| ?
if x-a >= 0 y = x-a
if x-a <= 0 y = a-x
Great
Now let’s consider a and b
a > b
|x-a|=|x-b|
You can make a little value table if you think it’ll help
here we have 3 case, right?
Exactly
hum
Now is the most important part
Once you tell me what you think I’ll give you an easy way on how to represent that
if x >= a, x-a = x-b <=> a = b
if a < x < b, a-x = x-b <=> x = a + b / 2
if x <= b, a-x = b-x <=> a=b
Be aware that a is bigger than b
Thé second would be then b < x < a
But otherwise it’s correct
Look :D
Now that this is understood
Let’s get back to the original problem
Which values do you think would be the best for a_1 and a_2 ?
we have : $\frac{x-a_1}{|x-a_1|+a_1} = \frac{x-a_2}{|x-a_2|+a_2}$
Exactly
0 and 1
Right
but it doesn't prove for all value
You said it’s common to all a ?
i means we can have a function that works only ofr 0 and 1
yeah
but proving with 0 and 1 would prove it just for 0 and 1
not for all a
Then there is one point that passed by f_a regardless of a ?
or we find a value with 0 and 1 and then we prove that it works for all a
then i'm ok
since a is not define it works ye
but how solve it
I’m going to try it first brb
What do you think about it
it seems weird
cause i took the value of a for x >= a into x <= a to find x
It’s not x/x that you have
if a = 0 what would we have then
Ohhh yeah
Well I have tested with a1 and a2
And made them equal to one and the other
And there is one solution
how do you found it
but we don't know if a1 > a2 or a2 > a1
It’ll be the same result
And we have to let one value bigger than the other
Also it doesn’t work if a is negative
Did you have something like that to solve
Nor if a = 0
hum why
Cause you’ll have some quadratic equations
and how do you solve it then
Eh i gtg, if I have the time I’ll explain it later
ok np thx anyway
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hi
if integers are consecute
then
they are just 1 more than the last one
so our numbers are: a,a+1,a+2,a+3
1/2 * n * (n + 1)
and we know the sum of the first three is 206
Sum of n first integers
a+a+2+a+3 works
Maybe you can use this to approximate the solution
find a form here
since a is an integer
we need to try all possible combinations
until a is an integer
and it works with this
with the other combinations a wont be an integer anymore
yes
yes
yes
you can check too if you want
np
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dont understand how f1(0) = 2, f1(1) = 4 etc...
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R is a subset of C. x is a member of R = (x, 0) is a member of C. we know that with the extended real line, x - infinite = negative infinite which should equal (x, 0) - infinite but isnt considered the case in this image. why is that?
well "positive" or "negative" wouldn't make sense in C anyway
essentially we just call all of them the same thing, just infinity. it doesn't matter in which direction you go
also as a sidenote, if x is in R, then x is also in C
if you want you can write it as x+i0 or something I guess but you don't need any tuples (x,0) here
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it is possible that A still does not contain 1 2 3 and 4
so while it is possible that A=N, there are also cases where A \neq N
So answer c and answer d are eliminated. We know for sure that 5 is an element of A, so answer b is still valid. Is there anything in the question to imply that 1, 2, 3, 4 are or are not elements of A?
Hey ik this isn't an answer but just a Lil curious if a is in the set then if a = 1, 2 will also be there as a + 1 is also in the set, and more, unless there is something else, cuz ik little about sets
So won't it be d?
but here they have said nothing about 1 being in the set
So I guess if A is out of the question the only possible answer is b. So was the whole 'If a is an element of A...' thing just a red herring?
sure, if 1 was in theset, then it would be d, but here 1 may not necessarily be in the set
we only know for a fact that 5 is in the set
ok i guess idk anything about sets, we only have that to study in our school from next year (Indian grade 10 student here btw)
Yeah I was trying to figure out why the a + 1 part is relevant but I guess it's just not
But I was almost convinced the answer was a because of that
pretty sure you'd have had some of it in grade 8 or 9
it is
it shows option (a) is correct
Idk if u are Indian but in our education system sets are only starting from grade 11
it basially shows A contains all natural numbers greater than or equal to 5
ok, different boards then
or I've just forgotten
But what if a = 1? Then 1 + 1 is 2 which is also an element of A
yeah, but the question says nothing about A
the question wants you to say what you know for certain
for certain from the question, we know A contains 5, as it says so
and we know that all integers greater than 5 are in A by the a+1 rule
Ohhh I see. We know for sure that 5 is in A, and if a + 1 is in A then every integer greater than 5 is also in A. We know nothing about integers <5. So b can't be true, neither can c or d. So the answer is a 🙂
Thanks a lot mate! Hope our boy Sharl wins the WDC next year! 😄
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I have an exam the day after tomorrow, this card is worth 1.5 in the final grade and I've been doing this shit since 8 in the morning
sqrt(3)=3^(0.5)
therefore
1/sqrt(3)=3^(-0.5)
now divide by this
wait
nvm
that is one step to much
just multiply by sqrt(3)
and then write sqrt(3) as 3^(0.5)
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i think i got it
damn, good luck bro
don't overdo it though, get godo rest
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How does this show that the Cardinality of N = Cardinality of Q
but what ive shown so far
how does that show that card N = card Q
Q+ at least, you can order the rationals
This means you can put them in order 1 2 3 …
sry bit lost
tbh
i dont acc understand
whats going on in the pic i sent
You’ve just put the rationals in a one-to-one correspondence with natural numbers
Hence showing their caardinality is the same
1:1
2:2
3:1/2
4:1/3
…
is the red column the reals?
and the blue row the rationals?
basically im confused on how this table is used to show that the card of N = card of Q
How do you show card N = card Z?
show that f is onto and 1-1
You can also show that you can arrange elements of Z in some order in a certain pattern.
0,-1,1,-2,2,…
You can count these and if i ask you what the 43th term is you can tell me which means there’s a one-to-one correspondence with the natural numbers.
can we go over the proof of #N = #Q from scratch together cuz im really confused icl
Do you get this
Z can be listed hence the same cardinality as N
It’s the same with the table you have. If you follow the direction of the arrow, eventually you’ll list all the rational numbers.
Do you get this
why have u ordered the Z in that way
We want to be able to list Z in a particular pattern so that we can guarantee every element of Z will appear on this list
This by listing we can call 0 the first term, -1 the second term, 1 the third term. This means there’s a one-to-one correspondence between N and Z.
but how does this show theres a one to one correspondence
There’s a function f that maps 1 to 0, 2 to -1, 3 to 1, 4 to 2 …
sry im just still confused why youve ordered z in that way
An infinite set is countable iff it’s possible to list all the elements in a sequence. This is because a one-to-one correspondence f from N to our infinite set can be expressed i terms of our sequence a1,a2,…,an where a1 = f(1), a2 = f(2),…an=f(n)
For example bijection from N to Z can be worked out quite easily by looking at our list
$f(n)=\begin{cases}
\hspace{1cm} \frac{n}{2} \hspace{0.89cm}\text{if n even}\
- \ \frac{n-1}{2} \ \ \ \text{if n odd}\
\end{cases}$
Pure
ok isee
imma watch a few videos and come back to u
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think i might have got it now
First we discuss how to compare the cardinalities (sizes) of two infinite sets. Then, we outline Cantors counterintuitive 1874 proof of the fact that the cardinality of (number of elements in) the infinite set of Natural Numbers (1, 2, 3, ) is exactly equal to the cardinality of the apparently much larger infinite set of Rational Numbers (all nu...
this video helped

thanks for the help
Np
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how would i find g(x)
You cant
so how would i go about this q
sandwich theorem
yea
Do you know what that is?
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Never faced a problem like this one. Would I multiply by the conjugate of 1/square root of x -5, or would I multiply the whole thing by the conjugate?
multiply 1/square root of x -5 by the conjugate of square root of x -5 over itself
are you able to visualize it here, I don't understand what you mean by "over itself"
multiply the left side by $\frac{\sqrt{x} + 5}{\sqrt{x} + 5}$
Gijs
i think that should get you further along
Left but not right, right?
multiply this by that fraction
Yeah, I get sqrt(x)+5/x-25
Anything afterwards?
continue to multiply by conjugate
so multiply numerator and denominator by sqrt(x)+5?
okay so you get then $\lim_{x \to 25} \frac{\sqrt{x} - 5}{x - 25}$
Gijs
this is what you have right
yes but you bring in the other fraction
i did that step for you
they have the same denominator now so you subtract 10
5 - 10 = -5
So wait, you merged both fractions?
yes
And since both fractions have a common denominator of x-25, you just kept one of those denominators and attached the numerator we just computed on top?
yes i think you understand
perhaps it would be good to write the steps out on paper though
Do you then substitute 25 in or multiply by conjugate again?
I GOT it.
1/10
how did you do it
wait
multiplied by the conjugate,got x-25 on numerator, canceled out x-25 on denominator and numerator, then got 1 on numerator and the square root of x +5.
I then substituted in 25 to find the limit, and simplified to 1/10.
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Hello, I was wondering if the answer I got for this problem is correct, Not really asking for the answer outright just want to know if I am correct, My answers for this is x = -1, x = -1/2, and x = 1. I would enter the answer myself but after many attempts I am now on my last try before the question locks itself from future attempts 😅
Well, by inspection we can see that x=1 is not a zero
2+3-1 =/= 0
So something's not right
true, i got it by quadratic formula and i was confused myself
guess ill recheck my notes
oh i got it right sick
welp thanks
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I am confused on what this means
a reference angle is the smallest angle made by the ray and the x axis
Right I get that
The trig values wouldn't be the same because they're just different angles?
Regardless of what quadrant they're in?
yes, the quadrant tells you which values to make positive or negative for the actual angle
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Hey, I need some guidance on how to solve this problem. I don`t if I have to use the conjugate method or do something else to get a and b.
use conjugates
Do i have to move the square root of 3 to the left?
no
Im stuck at a+bx-3/x(square root of a+bx+squareroot of 3)? Nothing is canceling out. Do i factor, distribute, or something else?
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no it hasn`t
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Hi, just a general question, if the vecteurs u, v, and w are linearly independent, would u+v, v+w and u + w are also linearly independent?
my intuition says yes they are still independent
but im not sure how to prove
maybe i can come up with something
lets check:
a(u+v)+b(v+w)+c(u+w)=0
au+av+bv+bw+cu+cw=0
u(a+c)+v(a+b)+w(b+c)=0
if this is equal to 0, then we have a,b,c pretty restricted
if we however say that u,v,w are linearly independent, then this should not work for any combinations
the wording at the end could be better
but i think this proves it
by contradiction
different wording:
let a+c=n, a+b=m, b+c=k
then we get:
nu+mv+kw=0
which is impossible since:
au+bv+cw=/=0 for all a,b,c
wait what do you mean by if "u,v,w are linearly independent, then this should not work for any combinations"