x=-8my=-6sin30°=-3r=√(x²+y²)=√(64m²+9)cosα=x/r=-8m/√(64m²+9)=-4/5√(64m²+9)>0所以-8m0√(64m²+9)=10m64m²+9=100m²m²=1/4m>0m=1/2