化简cos2α/tan(π/4+α)
问题描述：
化简cos2α/tan(π/4+α)
答
cos2a/tan(π/4+a)=cos2a/(tanπ/4-tana)/(1+tanπ*tana)=cos2a*(1+tana)/(1-tana)
答
cos2α/tan(π/4+α)
=sin(π/2+2α)/tan(π/4+α)
=2sin(π/4+α)cos(π/4+α)/[sin(π/4+α)/cos(π/4+α)]
=2cos^2(π/4+α)
=2[1+cos(π/2+2α)]/2
=1-sin2α