Question

Найдите sin2a,если sina=12/13 и а€(п/2;п)

Answer 1

sin(2a)=2sin(a)cos(a)

sin(a)=12/13 => cos(a)=-sqrt(1-144/169)=-sqrt(25/169)=-5/13

sin(2a)=-2*(12/13)*(5/13)=-2*(60/169)=-120/169