Question

[Lê Thảo Linh]

Chứng minh:

a)\(cot^2\alpha-cos^2\alpha\cdot cot^2\alpha=cos^2\alpha\)

b)\(tan^2\alpha-sin^2\alpha\cdot tan^2\alpha=sin^2\alpha\)

c) \(\dfrac{1-cos^2}{sin\alpha}\) = \(\dfrac{sin\alpha}{1+cos\alpha}\)

d)\(tan^2\alpha-sin^2\alpha=tan^2\cdot sin^2\alpha\)

e) \(\sin^6\alpha+cos^6\alpha+3sin^2\cdot cos^2\alpha=1\)