Question #e058f

Question

896 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-11-09T17:59:56

Use that dang ol' chain rule...

...but you have to apply it more than once...

$d/dx(cos^2(pi * x))$

$= 2cos(pi*x) * d/dx(cos(pi*x))$

$= 2cos(pi*x) * (-sin(pi*x) * d/dx(pi*x))$

$= 2cos(pi*x) * pi(-sin(pi*x))$

$=-2pi(cos(pi*x) * sin(pi*x))$

(Wolfram reminds me that you can use the double angle identity - $2cos(a)sin(a) = sin(2a)$ , so you can rewrite the above as:

$-pi(sin(2pi*x))$

GOOD LUCK