# How do you solve 10cos^2x - 5 = 1?

5[2${\cos}^{2}$ x - 1] = 1 $\implies$ 5 cos 2x = 1 $\implies$ cos 2x = 1/5 $\implies$ 2x = ${\cos}^{-} 1$ (1/5) $\implies$ x = (1/2)${\cos}^{-} 1$ (1/5)