(sina+cosa)/(sina-cosa)+cos2a(分子分母同时除以cosa)
=(sina/cosa+cosa/cosa)/(sina/cosa-cosa/cosa)+cos2a
=(tana+1)/(tana-1)+cos2a
=(2+1)/(2-1)+cos2a
=3+cos2a(万能公式 )
=3+(1-tan²a)/(1+tan²a)
=3+(1-2²)/(1+2²)
=3-3/5
=12/5
(sina+cosa)/(sina-cosa)+cos2a(分子分母同时除以cosa)
=(sina/cosa+cosa/cosa)/(sina/cosa-cosa/cosa)+cos2a
=(tana+1)/(tana-1)+cos2a
=(2+1)/(2-1)+cos2a
=3+cos2a(万能公式 )
=3+(1-tan²a)/(1+tan²a)
=3+(1-2²)/(1+2²)
=3-3/5
=12/5