Because of tenth (even) powers, P can never be negative. The maximum is achieved when |sin(x)| or |cos(x)|=1. In that case P=1. The minimum occurs when the terms are equal or $|\sin(x)|=|\cos(x)|=\sqrt{2}/2$. In that case P$=2^{-4}$. This gives a range for P $[2^{-4},1]$.