sin2a=2sinaсosa=2*(12/13)*(-(1-144/169))=-2*(12/13)*(5/13)=-120/169
ответ: -120/169
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
