Question

[Nguyễn Thùy Dương]

Rút gọn biểu thức:

a, A = \(\dfrac{4\sin^2\alpha}{1-\cos\dfrac{\alpha}{2}}\)

b, B = \(\dfrac{1+\cos\alpha-\sin\alpha}{1-\cos\alpha-\sin\alpha}\)

c, C = \(\dfrac{1+\sin\alpha-2\sin^2\left(45^o-\dfrac{\pi}{2}\right)}{4\cos\dfrac{\alpha}{2}}\)