Question

How do you solve `cosx(2cosx+1)=0`?

Answer 1

`cos x(2cos x + 1)=0` when either `cos x = 0` or `2cos x + 1 = 0`.

`cos x = 0` is true for `x = pi/2 + n pi` for all integer values of `n`.

`2cos x + 1 = 0` when `cos x = -1/2`

This is true for `x = (2n + 1) pi +- pi/3` for all integer values of `n`.