For $x^2 \neq n \pi+1, n \in N$ (the set of natural numbers), the integral $\int x \sqrt{\frac{2 \sin \left(x^2-1\right)-\sin 2\left(x^2-1\right)}{2 \sin \left(x^2-1\right)+\sin 2\left(x^2-1\right)}} d x$ is equal to : (where c is a constant of integration)