tính tích phân
a) \int_{0}^{\pi }\sqrt{1 - cos2x}dx
b) \int_{1}^{2}x\sqrt{x + 2}dx
c) \int_{\frac{\pi }{8}}^{\frac{3\pi }{8}}\frac{dx}{sin^{2}xcos^{2}x}
d)\int_{0}^{\frac{\pi }{2}}\frac{4sin^{3}x}{1 + cosx}