sin^2a+sin2acosa-cos2a=1 sin^2a+2sinacos^2a-1+2sin^2a=1 2sina(1-sin^2a)+3sin^2a=22sin^3a-3sin^2a-2sina+2=0(sina+1)(sina -2)(sina-1/2)=0∵a∈(0,兀/2) ∴sina=1/2tana=√3/3