(sina+cosa)/(sina-cosa)=2sina=3cosasina=3/√10 cosa=1/√10或者 sina=-3/√10 cosa=-1/√10sin(a-5π)*sin(3π/2-a)sin(a-5π) =-sinasin(3π/2-a)=-cosasin(a-5π)*sin(3π/2-a)= sina * cosa=3/10