Answer
$$\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\frac{x}{1+\cos ^{2}x}dx=0$$
Work Step by Step
$$let\ f(x)=\frac{x}{1+\cos ^{2}x}$$
$$f(-x)=\frac{-x}{1+\cos ^{2}x}=-f(x)$$
$$so, f(x)\ is\ odd$$
$$\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}f(x)dx=0$$