Question

[Lê Thanh Tuyền]

Câu 1: Chứng minh đẳng thức:

a)\(\frac{\sin a}{1+\cos a}\)=\(\frac{1-\cos a}{\sin a}\)

b)\(\frac{\cos a}{1-\sin a}\)=\(\frac{1+\sin a}{\cos a}\)

c)\(\frac{\cos a}{1+\sin a}\)+\(\tan a\)=\(\frac{1}{\cos a}\)

d) \(\frac{\sin a}{1+\cos a}\)+\(\frac{1+\cos a}{\sin a}\)=\(\frac{2}{\sin a}\)

e) \(\sin^4x+\cos^4x\)=\(1-2\sin^2x\cos^2\)x

f) \(\sin^4x-\cos^4x\)=\(1-2\cos^2x\)

g) \(\sin^6x+\cos^6x\)=\(1-3\sin^2x\cos^2x\)

h) \(\tan x\tan y\left(\cot x+\cot y\right)\)=\(\tan x+\tan y\)