how to solve y= 3cos2x + 5

Question

pls help me

Answer 1

Is that really cos(2x) or do you mean cos^2 x?

I will assume that you really do mean cos(2x). In that case

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

y = 6 cos^2x -3 + 5 = 6 cos^2 x - 2
cos^2 x = (y+2)/6
cos x = sqrt[(y+2)/6)]

You can use that to solve for x, if that is what the question is all about.

You cannot solve a single equation for both x and y.