Sin(α-π/4) , если...

Sin(α-π/4) , если cosα=-0.6, π/2<α<π.

 

Sin(a-p/4)
cosa=-0.6
p/2<a<p-2 четверть (Sin 2 четверти положителен)
найдем Sina
1-cost^2=sin^t
sin^2=(1^2-6/10^2)=(1-36/100)=(100-36/100)=64/100(  извлекли из квадрата )
sina=8/10   cosa=-0.6
sina*cos(-p/4)+cosa*sin(-p/4)
sina*cosp/4+cosa*sin(-p/4)
8/10*√2/2+(-6/10*-√2/2)⇒
4√2/10+3√2/10=4√2+3√2/10