Answer
$-1$
Work Step by Step
Let's take the derivative of both sides, and let's apply the fundamental theorem of Calculus (substitute the limits, and multiply by their derivatives) to both integrals on the right! $\frac{dy}{dx}=(\frac{1}{1+0^2}\cdot 0-\frac{1}{1+tan^2x}\cdot sec^2x)=-\frac{sec^2x}{1+tan^2x}=-1$