prove trigonometry

prove that [2Cos^2 (90－x)－1] / [Cos (90－x)－Cosx] =Sinx +Cosx
Sol
[2Cos^2 (90－x)－1] / [Cos (90－x)－Cosx]
= [2Sin^2 x－1] / [Sinx－Cosx]
= [2Sin^2 x－Cos^2 x－Sin^2 x] / [Sinx－Cosx]
= [Sin^2 x－Cos^2] / [Sinx－Cosx]
= Sinx+Cosx




2011-04-27 16:01:34 補充：
= [2Sin^2 x－Cos^2 x－Sin^2 x] / [Sinx－Cosx]
= [Sin^2 x－Cos^2 x] / [Sinx－Cosx]
= Sinx+Cosx