Найдите sinx*cosx, если sinx+cosx=2/5

(sin(x)+cos(x))^2=sin^2x+2sin(x)cos(x)+cos^2x=1+2sin(x)cos(x)=(2/5)^2=4/25 2 sin(x)cos(x)=4/25-1=-21/25 sin(x)cos(x)=-21/50=-0,42