CM BT ko phụ thuộc vào tham số x

\(A=2\left(cos^6x+sin^6x\right)-3\left(cos^4x+sin^4x\right)\)

B\(=\frac{tan^2x}{sin^2x.cos^2x}-\left(1+tan^2x\right)^2\)

Rút gọn các BT:

1) cos^2x+cos^2x.tan^2x

2) \(\frac{2cos^2a-1}{sina+cosa}\)

3) \(\frac{1-2sin^2a}{sina-cosa}\)

4) \(\frac{1+sina}{1-sina}-\frac{1-sina}{1+sina}\)

CM các đẳng thức LG sau:

1)\(\left(cos^4a+sin^4a\right)-2\left(cos^6a+sin^6a\right)=1\)

2) \(\frac{sin^2a+cos^2a}{1+2sina.cosa}=\frac{tana-1}{tana+1}\)

3) \(sin^4a+cos^4a-sin^6a-cos^6a=sin^2a.cos^2a\)

4) \(\frac{cosa}{1+sina}+tana=\frac{1}{cosa}\)

5) \(\frac{tana}{a-tan^2a}.\frac{cot^2a-1}{cota}=1\)