Cos(a+β)+sina*sinβ=cosa*cosβ-sina*sinβ+sina*sinβ=cosa*cosβ
cosa=-2/5
cosβ=15/16
cosa*cosβ=-2/5*15/16=-3/8
Ответ: -3/8
7х-3у-12=0
-3у= -7х+12
3у=7х-12
У=7/3х-4
У(3)= 7/3*3 -4= 7-4=3
Ордината точки равна 3
3x-π/7=π/2+πn 3x=π/2+π/7+πn=π(1/2+1/7)+πn=9π/14+πn
x=3π/14+πn/3