tanA=2
运用公式 sin2A=2tanA/(1+tan^2A)=4/5
sin^2A=tan^2A/(1+tan^2A)=4/5
则sinAcosA=sin2A/2 =2/5
(sinAcosA-sin^2A)/(1+3sinAcosA)=(2/5 -4/5)/(1+6/5)=-2/11