Question

How do you solve `cos^2x+2 cos x+1=0`?

Answer 1

`x = pi + 2k pi, {k = 0, pm1, pm2, pm3,...}`

Explanation:

`(cos x + 1)^2=cos^2x+2cosx+1=0`

then

`cos x+1=0`

`x = pi + 2k pi, {k = 0, pm1, pm2, pm3,...}`