【2（a-b）³-8（a-b）²（a+b）+6b（a-b）²】/2（a-b）²=【2（a-b）³-8（a-b）³+6b（a-b）²】/2（a-b）²=【-6（a-b）³+6b（a-b）²】/2（a-b）²=-3（a-b)+3=-...