a是第四象限角 sina0 且(sina)^2+(cosa)^2=1 [(4-2m)/(m+5)]^2+[(m-3)/(m+5)]^2=1 (4-2m)^2+(m-3)^2=(m+5)^2 4m^2-16m+16+m^2-6m+9=m^2+10m+25 4m^2-32m=0 m=0,m=8 代入sina=(4-2m)/(m+5)和cosa=(m-3)/(m+5) 则m=8符...