# proving using calculus without trig identity

by kebabs
Tags: calculus, hard, home work
 P: 4 Please I really need help with this hw question Prove without trig identity that f(x)=0 for F(x)=Asin^2(Bx+C)+Acos^2(Bx+C)
P: 791
 Quote by kebabs Please I really need help with this hw question Prove without trig identity that f(x)=0 for F(x)=Asin^2(Bx+C)+Acos^2(Bx+C)
You're not supposed to use the obvious identity that simplifies this? I suppose you could just use the derivatives of sin and cos along with the chain rule to directly compute the derivative. But eventually you'll need to simplify using some trig identity.
 P: 4 I can't use trig identy to solve it
P: 4

## proving using calculus without trig identity

I mean I'm not allowed to
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 Quote by kebabs Please I really need help with this hw question Prove without trig identity that f`(x)=0 for F(x)=Asin^2(Bx+C)+Acos^2(Bx+C)
What is F'(x) if $F(x)=A\sin^2(Bx+C)+A\cos^2(Bx+C)\,?$
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P: 1,338
 Quote by SteveL27 You're not supposed to use the obvious identity that simplifies this? I suppose you could just use the derivatives of sin and cos along with the chain rule to directly compute the derivative. But eventually you'll need to simplify using some trig identity.
Are you sure? I was able to get F'(x) = 0 by using the chain rule, and yet I didn't use any trig identity.
 P: 4 could you please send me your working for this question??
 P: 29 It's really simple - just use chain rule to take the d/dx of the whole expression. No trig or any other kinds of tricks necessary. Are you familiar with the use of chain rule?
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 Quote by kebabs could you please send me your working for this question??
This is not permitted at Physics Forums - don't even ask.

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