cos2x/(1+sin2x)=1/5 求tanx

cos2x/(1+sin2x)=1/5 (cos^2x-sin^2x)/(sinx+cosx)^2=1/5分子分母同除以cos^2x:(1-tan^2x)/(tanx+1)^2=1/55(1-tan^2x)=tan^2x+2tanx+13tan^2x+tanx-2=0(3tanx-2)(tanx+1)=0tanx=2/3或tanx=-1.tanx=-1时,x=180k-45,2x...