tanx=sinx/cosx
=(m-3)/(m+5) *(m+5)/(4-2m)
=(m-3)/(4-2m)
(m^2-6m+9)/(m^2+10m+25)+(16-16m+m^2)/(m^2+10m+25)=1
(m^2-6m+9)+(16-16m+m^2)=m^2+10m+25
m^2-32m=0 , m1=0 , (m2=32舍去）
tanx=-3/4 ,
x是第四象限,才能满足上述条件