1、1+cosx/1-cosx + 1-cosx/1+cosx=4cot^2x+2
问题描述：
1、1+cosx/1-cosx + 1-cosx/1+cosx=4cot^2x+2
2、sinx+tanx/cotx+cscx=sinx*tanx
恩有括号的那个
答
(1+cos x)/(1-cos x)+(1-cos x)/(1+cos x)通分=((1+cos x)^2+(1-cos x)^2)/1-cos^2(x)=2*(1+cos^2(x))/sin^2(x)因为1= cos^2(x)+sin^2(x)2*(1+cos^2(x))/sin^2(x)=2*(sin^2(x)+2*cos^2(x))/sin^2(x)=4cot^2(x)+2sinx...