(tanπ/4+tana)/(1-tanπ/4tana)=3
tanπ/4=1
所以tana=1/2
sina/cosa=tana=1/2
cosa=2sina
带入恒等式sin²a+cos²a=1
sin²a=1/5
原式=sina*(-cosa)-sin²a+1
=sina(-2sina)-sin²a+1
=-3sin²a+1
=2/5
(tanπ/4+tana)/(1-tanπ/4tana)=3
tanπ/4=1
所以tana=1/2
sina/cosa=tana=1/2
cosa=2sina
带入恒等式sin²a+cos²a=1
sin²a=1/5
原式=sina*(-cosa)-sin²a+1
=sina(-2sina)-sin²a+1
=-3sin²a+1
=2/5