sinα+cosα=√2/2
(sinα+cosα)²=1/2
1+2sinacosa = 1/2
sinacosa = -1/4

f(tanα)
= tana+1/tana
=(sin²a+cos²a) / sinacosa
=1/sinacosa
= -4=(sin²a+cos²a) / sinacosa怎么到这步的我没懂额tana+1/tana=sina/cos+cosa/sina通分之后就是了