Hãy đơn giản các biểu thức:
a) \(1-sin^2\alpha\)
b) \(\left(1-cos\alpha\right)\left(1+cos\alpha\right)\)
c) \(1+sin^2\alpha+cos^2\alpha\)
d) \(sin\alpha-sin\alpha cos^2\alpha\)
e) \(sin^4\alpha+cos^4\alpha+2sin^2\alpha cos^2\alpha\)
g) \(tan^2\alpha-sin^2\alpha.tan^2\alpha\)
h)\(cos^2\alpha+tan^2\alpha.cos^2\alpha\)
i) \(tan^2\alpha\left(2cos^2\alpha+sin^2\alpha-1\right)\)