For the second one, you need to know one identity in particular.

[4sin(x)cos(x)]cos(2x) = [2sin(2x)]cos(2x) = sin(4x)

Then, you solve for x.

For that, you find the first value of x as being the inverse of sine.

I'll call this angle alpha.

Then, you need to know in which quadrant sin is positive. It is positive in the first and second quadrant.

So, the value of 4x becomes 90 degrees.

Now, since x has a coefficient of 4, you need to consider 4 cycles, that is, you need to include 90+360, 90+720 and 90+1080.

This gives:

4x = 90, 450, 810, 1170 degrees

So, now you can find the value of x for each of those values. Note that I'm taking x to be within the interval of