- #1
jwxie
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Homework Statement
Simplify this expression.
sin(2* arcsin(x/3))
Homework Equations
The Attempt at a Solution
Let t = arcsin(x/3), we get sin(2t) which is double angle
sin(2T) = 2 sinT cosT
I did cosT first
T = arcsin x/3, and we know inverse of arcsin is sin T = x/3
this gives us the hypotenuse 3, and opposite side = x (3sin delta = x)
using the identity of cos^2 + sin^2 = 1, and solve for cos, I get cosT = sqrt(9-x^2)
This is corrected.
Now, solve for sinT.
sin(arcsin(x/3)), is the same as just x/3, by definition I think.
Well, the answer the book gave was 2x/9 * cosT
I get the cosT part right, but now the x/9
I don't understand how he produced the number 9.
Thank you. I have an exam so please pardon me posting so many questions these two days.