Giải:
\[A = \frac{\left( 1 - cotan^{2}(\frac{\pi}{2}+a\right))^{2}}{cotan^{2}(a - \frac{\pi}{2})\right)} = \frac{\left( 1 - tan^{2}a)^{2}}{tan^{2}a} = (\frac{1}{tana}-tana )^{2} \\ = (\frac{cosa}{sina} - \frac{sina}{cosa})^{2} = (\frac{cos^{2}a - sin^{2}a }{sina.cosa})^{2} = 4cotan^{2}2a\]
\[B = sin^6 (a-\pi ) + cos^6 (a -\pi)- 2sin^4 (a + 2\pi) - sin^4 (a+\frac{3\pi}{2}) + cos^2 ( a-\frac{\pi}{2})\\ = sin^6 a + cos^6 a - 2sin^4 a - sin^4(a+\frac{3\pi}{2}) + sin^2 a\]
tới đây bạn làm tiếp nha