Verified answer

tg a = sin a / cos a

tg a * cos a = sin a

cos a = sin a / tg a

cos a = 1/√10 * 3 = 3/√10

Ответ: Б

Verified answer

tg(x)=sin(x)/cos(x)  ⇔ cos(x)= sin(x)/tg(x)

cos(x)= (1/√10) /(1/3) =3/√10

Ответ : Б