Question

Calculati cos2x stiind ca x ∈ (0;$\frac{π}{2}$ ) si sinx = $\frac{ \sqrt{3} }{5}$

Answer 1

x ∈ (0  , π /2 )  in cadranul I sinx >0 si cosx>0
sin² x + cos²x =1 
( 3/5)² + cos²x =1 
cos²x = 1 - 9 /25 
cos²x = 16 /25 
cosx = 4/5