помогите sina+cosa=0,6 найдите sinacosa

sin(a)+cos(a)=0,6(sin(a)+cos(a))^2 = 0.36sin(a)^2 + 2sin(a)*cos(a) + cos(a)^2 = 0.361 + 2sin(a)cos(a) = 0.36sin(a)cos(a) = (0.36 - 1)/2sin(a)cos(a) = -0.32