#help-13
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say A = {(1,0), (0,1), (3,5)}, can you show me that A is not linearly independent? @errant wasp
a set is linearly independent when ....?
If the only solution is x = 0
were you thinking "when no vector is a multiple of another"? That's not the definition ๐
yeah unfortunately
you must have it in your notes?
If the only solution is x = 0 is linearly dependent
taken out of context that's a bit confusing, but it's saying this:
let W = {v1, v2, v3, v4...} be a set of vectors, x1, x2, ... be numbers, W is linearly independent when x1 v1 + x2 v2 + x3 v3 = 0 has only the solution x1 = x2 = x3 = ... = 0
then we can for sure abbreviate (x1, x2, ...) as just x, (0,0,0,0...) as simply 0, and say that a set is linearly independent when it has only x = 0 as the solution
It can be a bit abstract, because it's defined by the non-existence of something. To paraphrase, a set is linearly independent when there doesn't exist such not-all-zero x1, x2, ...,
Now can you tell me when is a set not linear independent?
at least one vector in the set can be represented as a linear combination of the other vectors in the set
hmmm that's indeed an equivalent defintion...not the one I'm asking though
but sure, do you understand what a linear combination is?
yes, earlier I avoided the term. But x1 v1 + x2 v2 + ... is exactly a linear combination of the vectors v1, v2, ...
Going back to this question, can you now try to represent a vector as a linear combination of the other two vectors?
(3,5)=3(1,0)+5(0,1)
that's great, and thus you have shown A is not linearly independent.
It's really just by constructing linear combinations.
It's especially easy in the cases when some are multiples of others, say {(3,4), (6,8)}. This set is not linearly independent just because (6,8) = 2 (3,4), the latter being a simple linear combination of one vector
its easier for me to see those examples tbh
sure, here is another one
a straight forward negation of the previous definition gives a equivalent form of "not linearly independent"
a set {v1, v2, ...} is not linearly independent when there exist not-alll-zero x1, x2, .... such that the linear combination x1 v1 + x2v2 + ... = 0
In this case, we can observe -3 (1,0) + -5 (0,1) + 1 (3,5) = 0
oh tats interesting
You can see how the two definitons are equivalent, we just need to move a term and divide both sides by a coefficient to represent a vector by the other vectors.
-3 (1,0) + -5 (0,1) + 1 (3,5) = 0
can become
-5 (0,1) + 1 (3,5) = 3 (1,0)
and it becomes
-5/3 (0,1) + 1/3 (3,5) = (1,0)
and hence we represented (1,0) using a linear combination of the other two vectors
thank you this was really helpful
no worries, linear algebra is fun ๐
can i ask another question?
sure thing
I see no problem in a)
okay i dont think i fully understand b
in b), you should understand what a projection is. The projection of a vector v, onto a space W, is roughly speaking, the part of v that's in W.
If v is already in W, then the projection is just v itself.
An example on a plane will be much helpful.
here, the green line is a subspace, say spanned by {(1,1)}
we have some purple vector
and the orange vector is the exactly the projection of the purple vector on to the green space. geometrically, it's obtained by drawing a perpendicular line to the green line starting from the arrow to the green line.
if a vector is already in the green subspace, projection onto the space just gives itself back.
because its already in itself?
here is an animation I made, hope it help you better understand the concept of projection
don't mind the labels, I meant to show u but didn't
the orange vector u1 is the projection of u onto the green subspace
The idea is like you are already asking for something to be in something when it is already the something thus it is returned
thank you for that visual
no worries, in general though, the subspace can be arbitrary, it can be a plane in R^3 for example, the same concept applies
take a random vector, shine a parallel light from afar perpendicular to that plane. The shadow on the plane is the projection of thatvector
if the vector is already on the plane, then the projection is itself
thank you so much
no worries
it's a special basis sastifying the orthonomal condition.
Recall a basis is
- linear independent
- spanning
but an orthonormal one has to be also - orthogonal
and 4. normal
3 means, every pair of vectors in that basis is orthogonal to each other (their dot product is zero, or geometrically, they are perpendicular)
4 means, each vector in that basis has to be "normal", meaning the length of every vector has to be 1
this is so much to remeber
the standard basis of R^2 {(1,0), (0,1)} for example ๐
P=A(A^T A) โ1 A^T what if A is an orthonomal basis
then is it like euqal to its identity
yeah the P = I actually. You have the trust the question that P is indeed a projection onto the column space of A. (This means for any vector v, P v is the resulting projection onto the space)
Since A is a basis now, the column space is just the whole space.
my notes say p = i is generall false tho
probably only works for orthonormal ones?
okay so you cant like assume p = i unless its orthonormal basically
oh wait
sorry I was assuming "A is a basis of the whole space"
P projects any vector in the space to the column space of A i guess in what i sent?
I think as long as A is a basis of the whole space, then P = I. The spanning property of the basis is the same as saying that the columb space of the basis is the whole space
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Hello i need help with the question F
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Hi I tried my best to try achieve the answer although I donโt know how and would appreciate some help
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Please help me with MATLAB code!!
I need to print out the iterates and the function values f(x_k) for secant method on the function f(x) = cosh(x/4)-x over the interval [-15,15] with the initial guesses x_0 = 0.5 and x_1 = 2.0
This is the code I have so far
format long
f = @(x) cosh(x/4)-x;
x_old = 0.5;
x_curr = 2;
tol = 1e-10; %error tolerance
i = 0; %iteration
N = 100; %max iteration
f_old = f(x_old);
while i <= N
f_curr = f(x_curr);
x_new = x_curr - f_curr*(x_curr - x_old)/(f_curr - f_old);
if abs(x_curr - x_old) < tol
fprintf('Solution is %f \n', double(x_curr))
fprintf('Number of iteration is %d \n', i)
return
end
i = i + 1;
x_old = x_curr;
f_old = f_curr;
x_curr = x_new;
end
Can you help me display the iterates and the function values please?
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Show your work, and if possible, explain where you are stuck.
How did you get 1/2?
Why a^4?
Can you show full work?
And the next step would be?
You have two equations, with two unknowns, solve for them
How did you solve for them
When someone asks you to show your work, you should show all your work, from start to finish
Then it's hard to help you without know what you did fully
My question is how did you get a = 1/2
You have two equations, how did you solve for a
Yes
This is the equation you should have gotten
You got a^4 = 1/16 the first time
$\frac{1}{2^3 \sqrt{2}}$?
dldh06
Then no
Because this doesn't have a cuberoot
So then what would a be?
$\frac{1}{2 \sqrt[3]{2}}$?
dldh06
This is what a is suppose to be
Because this is the proper equation
Yes
Yeah sounds right, but since you have a and C just plug those back in and see if it passes through the given points
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the equation is just z=0 right?
Yes
ty
@boreal flame Has your question been resolved?
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hi
@thorn sluice Has your question been resolved?
Well first you have to write each the line in vector form ๐ค
In a horizontal line, y is constant, and x is variable. What vector would represent that line? ๐ค
<0, x, 0>?
Wait that has 3 coordinates
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,w plot 8 + 6x -3x^2
Please don't occupy multiple help channels.
is this horizontal at 1?
U can verify by finding the vertex
The vertex is the peak/bottom of the parabola basically
here it'd be the peak
If the parabola points downward the vertex is the peak, if it goes upwards it's the bottom
ok?
do u know how to find a vertex
ok then yes it's horizontal at 1 
only at 1?
yeah
Mhm
can you help with this?
This is for calculus right
yeah
take derivative, that's ur line's slope
Then u can use point-slope form for convenience
To write the tangent line
how do i take the derivative
Uhhh why do you have homework that's making you do this if you haven't gotten to it yet
just curious
idk im just not good at math
this isn't about being good at math or not tho it's the barebones they teach u in Calc class
Do u know power rule?
like if u see $x^n$ alone
992qqoloy
Have they gotten to how u derive that yet
probs but i forgot
Well whenever u forget things u can always open ur textbook 
idk sorry if I'm being like this. I could just tell u the rule but this seems like a fundamental thing we can work on
So I guess either open ur book or google power rule that's what I usually do :p
so whats the derivative
I can't just tell u the derivative either solutions are against the rules 
Helpers in this server r just supposed to guide
is it -2x?
Yup
so do i plug 35 now?
Yup
so -20?
Yeah
yeah 2nd requires derivative
did i do the 1st one right?
yeah
Hmm even in the scenario where it would say 0.2 instead of 0.02 ur off by a 0
I think u misread the 0.02 as a 0.2 no biggie
Yee
p much the same as the first one
Yeah
I mean not the first part of this but the earlier problem using C(x)
36-0.04x
Yup
Mhm
Yup
Just dont plug in for t=1992
Gotta read the problem to figure out what t is supposed to be
25?
Yeah
Mhm
1.4x-13
yup
Yup
do i need to find the derivative?
yeah
For this 1 u can either expand and then derive each term
Or use product rule, but ull probably have to expand either way to put it in simplest terms
So I think it'd be easier to just expand it first 
oh ok
that makes sense
(12x^{8}-8x^{7}+10x^{5}-18x^{4}+12x^{3}-15x)
is this correct when expanding?
Yeah
ok
its the last one
96x^(7)-56x^(6)+50x^(4)-72x^(3)+36x^(2)-15
this is what i got
as the derivative
oh lmao
Yeah last one
quotient rule?
For this one there's the mnemonic "LowDeHigh minus HighDeLow over LowLow"
So $\frac{f(x)g'(x) - f'(x)g(x)}{g(x)^2}$
992qqoloy
The one that has the minus
Mhm
4.984
how many more of these are left cus i gtg
only a few more
itll be done quick
(-200(x^(2)-5))/((x^(2)+5)^(2))
for the first question is it 4.984?
or do i have to multiply it be a thousdands
since it says the population p in thousands
Actually that's a really good question
Problem doesn't say so I've no idea for sure
but yeah maybe multiply by 1000
ok
my 2nd answer is a negative decimal
-0.124
are we sure its 4984? or should we leave it as a decimal to three places
im gonna leave it as decimal i think
Aight
Yeah leave as decimal
Ic now that it says that at the bottom
https://www.wolframalpha.com/input?i=400t%2F(2t^2+%2B+10)+derive put your derivative into wolfram alpha just to double check 
yeah
im confused
what do i do after i found the derivative
since it isnt 1 of the answers but its close to all 4
oh wait is it C?
C includes all of it
Yeah
i didnt get 1/4
(x(2x^(2)-3))/(2(x^(4)-3x^(2))^((3)/(4)))
thats what i got
its A or D since 3/4 should be positive
yeah im confused
.close
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can some1 help
in a rush
v=ds/dt
a=dv/dt
derivative of s with respect to t
is it 14?
so then what is it
do you know what a derivative is?
no
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Iโm not sure how to start
log(ab) = log a + log b
Uh
Thatโs not what we used in class
I can show you a example similar to how my teacher did it?
if you did that for this question
youd be saying
4^64 = 4096x
if you put 4^64 into your calculator
it will not be nice
Is this what you meant by this
yes
then you can solve for log_4(4096) using change of base
do you know the change of base formula?
log_c a / log_c b
uh
yes
but notice
the base is the denominator
yes
ok you edited it
so
use change of base to evaluate log_4(4096)
okay but what do I put for the log_a (C) in the formula ? log_4 (X)
in log_4(4096)
4096 and x
so what is your base (b) and argument (c) for this
isnโt the base 4..? And the argument is 4096
yes
okay
now changing the base
its better to change the base to either e or 10 calculators usually compute logs with those bases
so putting it into the formula
youll get
oh wait sorry
$\frac{\log_{10}(4096)}{\log_{10}(4)}$
chef wang gang
now you can use a calculator to evaulate it for you
(as like i said calculators usually compute logs with base 10 or base e which is the purpose of change of base)
isolate the x? Right using the exponential form
-6 from both sides correct?
yep
log_4(x) = 58
now rewrite in exponential form
so you can get the solution for x
yep x = 4^58
Thanks so much
no worries
Sorry if I took a while to understand ๐
oh no no its perfectly fine
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hi,I'm having difficulty in this part, please help me.
help
chronic?
pronic?
๐ฟ
The question was translated by Google Translate because I'm not very good at English
post the original question.
original question in vietnamese:Cho x,y,z lร cรกc sแป thแปฑc khรดng รขm thแปa mรฃn x+y+z=6. Tรฌm giรก trแป nhแป nhแบฅt vร giรก trแป lแปn nhแบฅt cแปงa: P
just says "non-negative real numbers"
what section of your textbook are you on
and what class is this for, Multivariable Calculus?
(Calculus 3)
competition math i would guess
looks like plain inequalities man
It is for grade 9
yeah
ok so I have an equation of the derivative
let Z = 6 - X - Y
then
P = sqrt(X+Y) + sqrt(6-X) + sqrt(6-Y)
differentiate:
$\frac{dy}{dx} = \frac{(6-X)^{-1/2}}{(X+Y)^{-1/2} (6 - Y)^{-1/2}}$
Disorganized
um...
but we don't have Y only in terms of X
so idunno
else we could find the critical points
(maybe)
What is dx,dy?
nah nevermind
but the minimum maximizing values I think are X=Y=Z = 2 (by inspection)
I also think x=y=z but it's hard to convert it to the maximizing values
oh
there's a few ways to do this with P(X,Y) = sqrt(X+Y) + sqrt(6-X) + sqrt(6-Y)
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practice exam
why is this the case
I undersatnd finding x if its minimal
but not largst
Product of LCM and HCF of two numbers is equal to their product
ye
you want the largest x such that x =/= lcm(x, y)
but by definition, x divides lcm(x, y)
so x is the largest divisor of lcm(x, y) different from lcm(x, y)
since lcm(x, y) is divisible by 2, x is necessarily lcm(x, y)/2
since you can't divide lcm(x, y) by less than 2 without x being equal to lcm
why can't x just be the lcm(x,y)
sorry for ping hope its ok but
similar question
but why is it 3^2 not 3?
because 3 is not in the gcd, so it divides only x or y but not both
so among x and y, one is divisible by 3ยฒ = 9
hm
if x = lcm/3, y would divide 3, so be 1 or 3, but both are impossible
@honest bobcat Has your question been resolved?
sorry for another tag iโm really tryna get this shit ๐ญ
would you be able to elaborate a bit more
on maybe a general example too
nw if not
you want the largest x different from lcm(x, y)
but gcd(x, y) divides x and x divides lcm(x, y)
so can we choose x = lcm/2 ? no, because then 2ยฒ doesn't divide x, so gcd(x, y) wouldn't divide x
the gcd and lcm put constraints on our choices
could we take x = lcm/3 ?
no, because then 3 would divide x and y, but then it would divide gcd(x, y)
but 3 doesn't divide gcd(x, y)
you could say well then, I will take lcm/5, it's larger than lcm/9
but it still doesn't work for the same reason
5 can't divide both x and y
since it doesn't divide gcd(x, y)
ahh this makes sense here, that would give x a factor of 3, but because the lcm contains another factor of 3 it has to come from y?
because the whole 3 as a prime factor get put into the x
so we don't have to make it appear in y
nor in gcd(x, y)
@honest bobcat Has your question been resolved?
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is this how we differentiate
im still not familiar with this notation
@lavish jolt Has your question been resolved?
@lavish jolt Has your question been resolved?
Can you describe in words what you're trying to write? It's a bit confusing as written
@lavish jolt Has your question been resolved?
Im trying to derive the lagrangian density
A_ฮผ is a vectorial field
thats one term of the expression
@lavish jolt Has your question been resolved?
@lavish jolt Has your question been resolved?
@lavish jolt Has your question been resolved?
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hi guys i want to get โvโ from this equation, please help
$mg(h-h_0) = \frac12 m(v^2 - v_0^2)$
Ann
!status
What step are you on?
1. I don't know where to begin
2. I have begun but got stuck midway
3. I got an answer but I'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
3
show work
(though i fear i might have a hard time reading it with this heavy cursive you've got...)
its not important
anyway, line 3 seems to be wrong
or like
... even number of mistakes, i guess?
you added v0^2 into the fraction in a bullshit manner, and then you cancelled out the m's in a bullshit manner.
but you ended up with $2g(h - h_0) + v_0^2 = v^2$?
Ann
which seems correct to me
but then you square rooted both sides and
somehow $\sqrt{2g(h-h_0) + v_0^2}$ became $\sqrt{2g + v_0^2 (h - h_0)}$?
Ann
why did the $v_0^2$ get a 2 coefficient?
Ann
i dont know i thinks its correct that way
thanks for helping btw
give me a sec i try something
This is my process๐
math is hard
and how is it correct then? i am lost
@tropic oxide can you please tell whats wrong?
the one i can see and point out immediately is that you rewrite a/b + c as (a+c)/b
it is hard for me to point it all out since there is so much of it and it piles on top of each other
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hey
f(x)=ax^3-8x^2+bx+6
f(x) is divided by x+1
there is no remainder
f(x) is divided by x-2 the remainder is x-12
what is the value of a and b???????
do you know your remainder theorem
so what do I do ?
So first if x+1 divides f(x) then what can you say about -1 with respect to f(x)
f(-1)=a(-1)^3-8(-1)^2+b(-1)+6
-a+8-b+6
ok nice
now i am telling you that x+1 divides f(x)
so f(x)=(x+1)(something)
isnt this right
that something is also a polynomial
now what is f(-1) from here
-a+8-b+6
?
just sub -1
i asked from here
not from the original expression of f(x)
f(-1)=(-1+1)(something
which is
why +8
ok great
so f(-1)=-a-8-b+6=0
exactly
now we use the other part of the given to get another equation in a and b
we can translate second part of the equation to f(x)=(x-2)(some other thing)+x-12 so f(2)=??
do you know how i got to this ?
remainder of division of f by x-2 is x-12
f(2)=(2-2)(?)+x-12
=??
ok you have 2 simultaneuous eqs now solve the system to find a and b
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Wouldnt A1xA2 be {(0, 0๏ผ(0,1 }๏ผ
yes
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i need help for finding if something is a subspace of R^n or not
Anyone know a resource to help me learn this. im really stuck
please use reply to notify me
reply text:
https://textbooks.math.gatech.edu/ila/subspaces.html
reply video:
https://www.khanacademy.org/math/linear-algebra/vectors-and-spaces/subspace-basis/v/linear-subspaces
uh well that's not what i meant by reply hah
but thanks
are you aware if this covers enough examples?
AMAZING
thank you so much
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hello there Peter!
your g(x) is just f(x-1), which is only shifting f(x) to the right side by 1
My method would be first move to graph so that we can move x=1 to x=0, and do it like normal reflecting along x=0, and finally move it back
@crimson sedge Has your question been resolved?
christ you're good at dutch, peter
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How to write a closed formula for the following series
,rotate
$2, 2+7(1), 2+7(2), 2+7(3), ...$
deltaG
but it's not that
wait nvm I'm stupid
lmao no worries
||2+7*2^(n-1)||
could you explain how you got to this formula?
i should mention that the first item in the series is u_0
the formula is close but not quite
such that n = 0
then of course it's different
yeah sorry i forgot about that until now
instead of trying it via the common difference, subtract 2 from the original sequence and divide by 7. then you'll obtain another sequence for which finding a closed form should be much easier
ok i'll try that out and then given an update if i still have any more doubts
(the numbers 2 and 7 being motivated from the common difference attempt, they arent completely out of nowhere)
yeah i got that, thanks!
ok wait
my problem got "reassigned"
i have a very similar sequence
and i've noticed soething else about this one
and i can make the general sequence:
2 + n(11*3^(n-1))
well that was wrong
anyway, thanks for the help!
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Can I get help solving these? Iโm canโt do the steps. The answer is 31,125
How do we combine fractions with two different denominators?
Yep so whatโs the lcd of 8 and 12
Ok so how do we change the fractions to have that denominator
The first multiplied by 12 and the second multiplied by 8?
Close but you have do 12/12 and 8/8
So the top and bottom are both multiplied by 12 for the first fraction and the top and bottom of the second are multiplied by 8
So do that work and lmk what you got
Yes okay now we can combine the like fractions
?
So it will just be one big fraction over 96
Ohhh ok Iโll do that rn
Since the denominators are the same you can add the numerators together
Lmk what you get
๐
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range of f = possible ys
notice that
2|3-x| >= 0 for all real x
in other words if it was f(x) = 2|3-x| its range would be [0, inf)
since modulus is nonnegative
and whats that
so i would write ranges for f are x is bigger than or equal to 0
range is about values of the function, so it's about "y"
not x
I guess you don't understand what I'm trying to say
look at this simple example
let's say we want to state range of |x| + 1
knowing that |x| >= 0 we can easily deduce that |x| + 1 >= 1
so then in this case of 2|3-x|+5 >= ?
ee not really
you don't have to solve anything to get the range
it isn't an inequality you're supposed to solve
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my mom wants to put wallpapers on the walls, we need 30 cubic meters, one wallpaper is 30x35cm how much do we need?
how much cm^2 is a wallpaper?
you mean square meters, right?
yes
30x35cm
idk the square meter for that
im sorry
and then figure out the whole wall in cm^2, and divide
you have to change both in the same form, so we could see the ratio
1 m^2 is how many cm^2?
why
@clever kite Has your question been resolved?
no.
why not tho
ok then help me solve it
ohhh
3000x3500?
is 6500cm2
so i need 65m2?
wait waht
no again
lemme thnik
that was dumb as hell
wait
30x35 is 1050
so one wallpaper is 1050cm2?
doesnt look right tho
ok so thats 10.5m2
the wall is 30m2
divide?
so i need 2.8 wallpapers?
so i should buy 3?
doesnt look right more
no
now you just have to put the 2 info together
im lost
Its just algebra from this point
Write an equation
You know how much cm2 the 30 m2 is
And what is the wallpapers area
yes
dont say this
if you do not see the solution from the start its not bad, you just need small steps towards the answer using what we know at that point (it doesnt hurt to make a list os these infos separately)
but whats the x
unknown
the number of wallpapers in this case
you dont know how to solve equations?
u should have met with equations then, no?
oh, sry
my mistake, i forgot the original Q
so 30 m^2
and we know 1 is 10000 cm^2
so 30 is 300000 , the square is on the cm not the number
see? thats why we need to always doublecheck : D
im still confused
with what? please dont just say youre confused and leave it there like that
everything is confusing me
i wish i could tell you with what
but my only response is everything
oh boy
yea
xd
but if you line them up i can try to go through the math related ones
anyway the answer is 30 * 10000 / 1050
still stuck with that the 1 wallpaper is 1050 square cm and the wall is 30 square metres
30 mห2 is 300000 cm^2
still the answer is 8571
how??
look at it, it should not be higher than 300
glad if i could help
next time try to sit on it a bit, and come here with more specific questions, it should make thing faster/easier
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The height of the base of a regular triangular prism is 2โ3cm. Find the area of โโthe lateral surface of this prism if the diagonal of the lateral face of the prism forms an angle of 30โฆ with its lateral edge.โ need help with a solution
How?
it can not be true
Okay, man...
Please actually try to help the dude if you know how
Don't waste his time and disappoint him.
What does this mean by "height of the base"?
Oh okay, I see it. The yellow was too light
height of triangle
yes
Okay.... and that's the area we need to find, right?
Gotcha...
Do you know basic trigonometry?
i think yes
Okay, so if you look at the triangle that the 30 degree line forms...
What would the adjacent and opposite lengths be? (Don't need an exact value, just give me the expression itself)
like Length(A, B1) * sin (angle)
Something like that
sin(30)*ABB1?
sin(30)/ABB1
Yes
What's:
length(A, B)?
length(B, C)?
...in terms of length(A, C)
(A,B) = tg
or not? I don't quite understand your question
Okay, I'm writing it in a way more complicated way.
I'm asking:
What's length of AB?
What's length of BC?
Give me an equation for each of them, using length AC
AB=BC/AC=cos
BC = AB/AC=tg
like this?
firstly... what the frick is "tg"? ๐
No...
tan
what do soh cah and toa mean???
Sin(angle) = Opposite/Hypotenuse
Cos(angle) = Adjacent/Hypotenus
Tan(angle) = Opposite/Adjacent
remember this: opposite means the angle doesn't touch the line. Adacent means the angle does touch the line
ok
I understand it
Okay, wonderful.
So sin(angle) = opposite/hypotenuse can be rearranged as:
hypotenus * sin(angle) = opposite
if you know how to do a bit of algebra.
yes
Similarly,
cos(angle) = adjacent/hypotenuse
so
hypotenus * cos(angle) = adjacent
yes
So this becomes:
AB = AC * sin(12)
BC = AC * cos(12)
Understand?
yea
Okay, now apply this to your question.


