Найдите sin2α,если cosα= -5/13 и π/2< α <π

Question

Найдите sin2α,если cosα= -5/13 и π/2< α <π</p>

Answer 1

cos2х=cos^2х-sin^2x=2cos^2x-1

 

2*(-5/13)^2=-50/338

 

Answer 2

...........................

---