👤

Calculati cos 2a , stiind ca tg a/2= 2

Răspuns :

[tex]\displaystyle\cos a=\frac{1-\tan^2\frac{a}{2}}{1+\tan^2\frac{a}{2}}=-\frac{3}{5}[/tex]
[tex]\displaystyle\cos 2a=2\cos^2a-1=-\frac{7}{25}[/tex]