# Math Help - sin(4x)*cos(x) = 0.84

1. ## sin(4x)*cos(x) = 0.84

I am having a hard time with this problem. The only thing I can think to do is change cos(x) to (1-sin^2(x)) but im not even sure how that would help. What step am I missing here?

2. $\color{blue}\boxed{\sin(4x) = 2\sin(2x)\cos(2x)}$

and

$\sin(2x) = 2\sin(x)\cos(x)$

and

$\cos(2x) = \cos^2 (x) - \sin^2 (x)$

also please notice that cos(x) is not equal to 1-sin^2x

but

$\cos^2 (x) = 1 - \sin^2 (x)$

3. Thank you. However, I am still having problems.

Sin(4x) * Cos(x) = 0.84
2*Sin(2x)*cos(2x) * cos(x) =0.84
2*2*Sin(x)*cos(x)*(cos^2x-sin^2x)*cos(x) = 0.84
4*sin(x)*cos^2(x)*(cos^2x-sin^2x) = 0.84
sin(x)*cos^2(x)*(cos^2x-sin^2x)=0.21

Forgive me, but I am not sure how to further simplify this problem.