sina/cosa=tana=2
cosa=1/掘陪2*sina
代入恒等式sin²a+cos²凳纳a=1
sin²a=1/5
sinacosa=sina(1/2*sina)=1/2*sin²判粗蠢a=1/10
所以原式=21/10
sin^2a-sinacosa+2
＝做瞎孝碧（纯慎空2sin^2a-sinacosa+cos^2a）/(sin^2a+cos^2a)
=(2tan^2a-tana+1)/(tan^2a+1)
=(8-2+1)/(4+1)
=7/5
sin^2a-sinacosa+2=cos^2a(tan^2a-tana)+2=[1/数运晌让(sec^2)](tan^2a-tana)+2=[1/(1+tan^2a)](tan^2a-tana)+2=[1/薯谨梁(1+2^2)](2^2-2)+2=12/5
tana=2,cota=1/2
sin^2a=1/唯判csc^2a=1/(cot^2a+1)=1/(1/4+1)=4/5
sinacosa=1/指空改2sin2a=1/2*2tana/(1+tan^2a)=2/1+4=2/5
所以亏租原式=4/5-2/5+2=12/5