1/tana+ tana =5/2, tana=2或1/2.原式=(2sin²a-3sinacosa+2)/( sin²a+cos²a)=(4sin²a-3sinacosa +2 cos²a)/( sin²a+cos²a)=(4tan²a-3 tana+2)/( tan²a+1)=12/5或6/5.
