Question

Can someone help me solve this problem:

cos^2x + 5cosx - 2= 0

I am having some trouble finding x

Answer 1

treat it as a quadratic equation where

cosx = (-5 ± √(25 - 4(1)(-2))/2
= .37228 or -5.37..
The second answer lies beyond the range of the cosine function so
cosx = .37228 and x must be in the first or fourth quadrant.
x = 68.14 degrees or 291.86 degrees.

in radians it would be x = 1.18933 or 5.09385