sinθ+cosθ=－（根号10）/5两边平方(sinθ)^2+2sinθcosθ+(cosθ)^2=2/51+2sinθcosθ=2/5sinθcosθ=-3/10[(sinθ)^2+(cosθ)^2]/(sinθcosθ)=1/(sinθcosθ)=-10/3[(sinθ)^2+(cosθ)^2]/(sinθcosθ)=(sinθ)^...