该题应该是10y^2,不是10x^2
kx^2-9xy-10x^2=（mx+2y)(3x-5y),
kx^2-9xy-10x^2=3mx^2-5mxy+6xy-10y^2
kx^2-9xy-10x^2=3mx^2-10y^2+xy(6-5m)
k=3m
-9=6-5m
m=3
k=9