ngoclan281098

1. $tan^{2}x+3=\left ( 1+\sqrt{2}sinx \right )\left ( tanx+\sqrt{2}cosx \right )$

2. $cosx - cos7x =3\sqrt{3}sinx$

3. $\frac{\sqrt{2}\left ( sinx-cosx \right )^{2}\left ( 2sin2x+1 \right )}{sin5x+sin3x}= 1-tanx$