# Math Help - Derivatives of Trig.

1. ## Derivatives of Trig.

Hi!
The question is to find the derivative of:
0.5 sin2x + cosx for 0 < x < 2pi

My answer is:
sinx + 0.5 cos 2x, but I am not sure if it's correct.
Thanks in advance,
Amine

2. Originally Posted by Aminekhadir
Hi!
The question is to find the derivative of:
0.5 sin2x + cosx for 0 < x < 2pi

My answer is:
sinx + 0.5 cos 2x, but I am not sure if it's correct.
Thanks in advance,
Amine
$
\frac{d}{dx} \sin(ax) = a\, \cos(ax)$

The derivative of cos is -sin and you forgot the chain rule on the sin(2x) term

$
\frac{d}{dx}[0.5\sin(2x)+ \cos(x)] = \cos(2x)-\sin(x)$