求证sin^2a*tana+cos^2a*1/tana+2sina*cosa=tana+1/tana
问题描述：
求证sin^2a*tana+cos^2a*1/tana+2sina*cosa=tana+1/tana
答
sin^2a*tana+cos^2a*1/tana+2sina*cosa
=(1-cos^2a)*tana+(1-sin^2a)*1/tana+2sina*cosa
=tana-sina*cosa+1/tana-sina*cosa+2sina*cosa
=tana+1/tana