已知sin^2a+sin2acosa-cos2a=1,a∈(0,π/2),求sina,tana的值sin^2a+sin2acosa-cos2a=1=sin^a +cos^asin^2a+sin2acosa=cos^a-sin^a+sin^a +cos^a=2cos^a4sin^acos^a+2sinacos^a=2cos^a2sin^a+sina=1(2sina-1)(sina+1)...