sin²θ+cos²θ=1[(m-3)/(m+5)]²+[(4-2m)/(m+5)]²=1(m-3)²+(4-2m)²=(m+5)²m²-6m+9+16-16m+4m²=m²+10m+254m²-32m-0m=0或m=8(1) m=0,sinθ=-3/5 与θ∈(π/2...sinθ=-3/5 与θ∈(π/2, π),为什么矛盾θ∈(π/2, π),sinθ>0所以矛盾