(x+y+z)^3=0如果你不知道三项的展开式的话 先把x+y看成一项（x+y+z）^3=(x+y)^3+z^3+3(x+y)^2z+3(x+y)z^2=x^3+y^3+z^3+3x^2y+3xy^2+3(x+y)^2z+3(x+y)z^2=x^3+y^3+z^3+3xy(x+y)+3(x+y)^2z+3(x+y)z^2=x^3+y^3+z^3+3(x+...