为表达方便,设tanx=t=2sin2x=2t/(1+t^2)=4/5cos2x=(1-t^2)/(1+t^2)=-3/55sinx^2+3sinxcosx-2cosx^2=3sinx^2+1.5sin2x-2cos2x=1.5(1-cos2x)+1.5sin2x-2cos2x=1.5+1.5sin2x-3.5cos2x=24/5