How Many Solutions Does $\cos ^{4} \theta-\sin ^{4} \theta=\frac{1}{3}$ Have For $0 \leq \theta \leq 4 \pi$

Short Answer

How many solutions does $\cos ^{4} \theta-\sin ^{4} \theta=\frac{1}{3}$ have for $0 \leq \theta \leq 4 \pi$ ?