Let $a, b \in R, b \neq 0$, Define a function $f(x)\left\{\begin{array}{cc}a \sin \frac{\pi}{2}(x-1), & \text { for } x \leq 0 \\ \frac{\tan 2 x-\sin 2 x}{b x^3}, & \text { for } x>0\end{array}\right.$. If $f$ is continuous at $x=0$, then $10-a b$ is equal to $\_\_\_\_$ .
