tinh tanx/2 biet cosx=4/5

Đáp án:

cos$\frac{x}{2}$ =$\sqrt[]{\frac{1+cosx}{2}}$ =$\frac{3\sqrt[]{10}}{10}$ 

sin$\frac{x}{2}$ = $\sqrt[]{1-cos²\frac{x}{2}}$ = $\frac{\sqrt[]{10}}{10}$ 

⇔ tan$\frac{x}{2}$=$\frac{sin\frac{x}{2}}{cos\frac{x}{2}}$ =3

Hok tốt !