Trigonometric differentiation

  • Thread starter h_k331
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  • #1
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When y=sin(pi*x), why does y'=cos(pi*x)*pi, not y'=cos(pi*x)?

hk
 

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  • #2
Integral
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It's the chain rule. when the argument of a trig function is a FUNCTION of x, you have take the derivative of the agrgument. So, in general

(f(g(x)))'= f'(g(x))*g'(x)
 
  • #3
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So than in this case y=f(u)=sinu and u=g(x)=pi*x, correct?
 
  • #4
OlderDan
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h_k331 said:
So than in this case y=f(u)=sinu and u=g(x)=pi*x, correct?
That is correct.
 
  • #5
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Thanks guys, I appreciate it.

hk
 

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