m^2=(x-y)^2 = x^2+y^2-2n（x³+y³）² = [(x+y)(x^2-xy+y^2)]^2 =[(x+y)(m^2+2n)]^2=(x+y)^2(m^2+2n)^2（x³+y³）² = (m^2+4n)(m^2+2n)^2