(a-b)(a^2+b^2+ab)/3-a^2b+ab^2=(a-b)^2,且a不等于b求a-b的值

(a-b)(a^2+b^2+ab)/3-a^2b+ab^2=(a-b)^2(a-b)(a^2+b^2+ab）-3a^2b+3ab^2=3(a-b)^2(a-b)(a^2+b^2+ab）-3ab（a-b）=3(a-b)^2(a^2+b^2+ab）-3ab=3（a-b）a^2+b^2-2ab=3（a-b）（a-b）^2=3（a-b）a-b=3