Proving using calculus without trig identity

  1. 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)
     
  2. jcsd
  3. 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.
     
  4. I can't use trig identy to solve it
     
  5. I mean I'm not allowed to
     
  6. SammyS

    SammyS 8,876
    Staff Emeritus
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    What is F'(x) if [itex]F(x)=A\sin^2(Bx+C)+A\cos^2(Bx+C)\,?[/itex]
     
  7. eumyang

    eumyang 1,347
    Homework Helper

    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.
     
  8. could you please send me your working for this question??
     
  9. 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?
     
  10. Mark44

    Staff: Mentor

    This is not permitted at Physics Forums - don't even ask.
     
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