calculus - How to calculate $lim_{xto 0}left(frac{1}{x^2} - frac{1}{sin^2 x}right)^{-1}$?

$$f (x) = \frac{1}{x^2} - \frac{1}{\sin^2 x}$$

Find limit of $\dfrac1{f(x)}$ as $x\to0$.