Question

\[f'(x)=-4sinx-2\sin2x\]\[=-4sinx-4sinxcosx\]\[=-4sinx(1+cosx)\]

Please explain to me, why this is so?
Especially how you get from the first step to the second step.

Answer 1

sin 2x = 2 sinx cos x
this comes from angle sum formula
sin(x+x) = sinxcosx + sinxcosx = 2 sinx cosx

Answer 2

Thanks dumbcow!

Answer 3

:)