t - в 1-ой четверти
sin²t+cos²t=1
cos²t=1-(4/5)=1-16/25=25/25- 16/25=9/25
cost=√(9/25) =3/5
sin2t=2sintcost=2* 3/5 *4/5=24/25
cos2t=cos²t-sin²t=(3/5)²-(4/5)²=9/25-16/25= -7/25
