已知已知cos（π/4+x）=5/13,且0

已知0＜x＜π/4,sin(π/4-x)=5/13,求cos2x/cos(π/4+x)的值已知0＜x＜π/4,则sinx>0,cosx>0sin(π/4-x)=sinπ/4·cosx-cosπ/4·sinx=√2/2(cosx-sinx)=5/13则cosx-sinx=5√2/13,又因为sin²x+cos²x=12cosx...