9. The smallest positive period of the function $y=\sin ^{2 n} x-\cos ^{2 m-1} x\left(n 、 m \in \mathbf{N}^{-}\right)$ is $\qquad$
9. $2 \pi$. According to the odd and even function method. It is easy to prove that the minimum positive period of the even function $y=\sin ^{2 n} x$ and the odd function $y=\cos ^{2 \pi+1} x$ are $\pi$ and $2 \pi$, respectively, and their minimum positive period is $2 \pi$.