2x^3-7x^y+5xy^2+14y^3=3(x^3-3x^2y+2xy^2+3y^3)-(x^3-2x^2y+xy^2-5y^3)=3m-n如有疑问，可继续追问
2x^3-7x^y+5xy^2+14y^3的值是3m-n
