# Math Help - calculus and trigonometry

1. ## calculus and trigonometry

If f(x) = (ax + b) sinx + (cx +d ) cosx
find constants a, b, c, d, such that f'(x) = xcosx

How do I do this?

thanks

2. Originally Posted by differentiate
If f(x) = (ax + b) sinx + (cx +d ) cosx
find constants a, b, c, d, such that f'(x) = xcosx

How do I do this?

thanks
Find the derivative and set it equal to $x \, cos(x)$. Then, solve the last equation for a,b,c and d.