tana+1/tana=9/4,则tan^2+1/sinacosa+1/tan^2a=?
问题描述:
tana+1/tana=9/4,则tan^2+1/sinacosa+1/tan^2a=?
答
sina/cosa+cosa/sina=9/4=1/sinacosa ,(sinacosa)^2=16/81tan^2+1/sinacosa+1/tan^2a=sin^2a/cos^2a+9/4+cos^2a/sin^2a=9/4+(sin^4a+cos^4a)/sin^2acos^2a=9/4+[(sin^2a+cos^2a)^2-2(sinacosa)^2]/(sinacosa)^2=9/4+...