The integral is basically \int_{0}^{\frac{\pi}{4}}\frac{cos2x\sqrt{1-sin2x}}{2-sin2x}dx=\int_{0}^{\frac{\pi}{4}}\frac{sin2x\sqrt{1-cos2x}}{2-cos2x}dx
Take cos2x=k, from which we have l.\int_{\frac{1}{2}}^{1}{\frac{\sqrt{2k-1}}{2k}dk}
Where l is a const.
Now it is easy...