Posted by **emily** on Tuesday, May 18, 2010 at 6:56am.

how to solve y= 3cos2x + 5

pls help me

- math -
**drwls**, Tuesday, May 18, 2010 at 8:21am
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.

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