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## Homework Statement

Solve the following trigonomic equation for 0<=x360<= :

5cos2x + cosx + 2 = 0

## Homework Equations

Not sure what goes here but I've been trying to substitute these -

cos2x = cos^2x - sin^2x

cos2x = 2cosx^2 - 1 - I think this is the correct one to use.

cos2x = 1 - sin^2x

## The Attempt at a Solution

5cos2x + cosx + 2 = 0

5(2cos^2x-1) + cosx + 2 = 0

10cos^2x + cosx - 3 =0

cosx (10cosx +1) - 3 = 0

? I get stuck here

Am I going about this the right way, or am I completely lost? I think I'm doing it right, I'm just not sure how to continue.

Any help appreciated.