Question

Find all solutions to the equation.
cos2x + 2 cos x + 1 = 0

This is how far I got. I'm stuck, please help.
cos^2x + 2 cos x + 1 = 0
=> cos^2x = 2cos^2 x - 1
=> cos2x = 2cos^2x - 1

Answer 1

let m=cosx, so essentially your equation is: \(\ m^2+2m+1=0 \)
notice this is a quadratic... u remeber how to solve quadratics?