tana+1/tana=3可化成sina/cosa+cosa/sina=3 化简 得sin^2a+cos^2a /sinacosa=3可得出 sinacosa=1/3 由此可得出 sina+cosa=根号15/3 cosa-sina=根号3/3sina*cosa tan^2 a+1/tan^2 a=sina*cosa (1-cos^2a +sin^2a/1+co...