sina+cosa=1/3平方
(sina+cosa)²=1/9
sin²a+cos²a+2sinacosa=1/9
1+2sinacosa=1/9
2sinacosa=-8/9
sinacosa=-4/9
tana+cota
=sina/cosa+cosa/sina
=sin²a/cosasina+cos²a/sinacosa
=(sin²a+cos²a)/sinacosa
=1/sinacosa
=1/(-4/9)
=-9/4