=1/9 a的6次方b的4次方 ×(-8a³b的6次方)÷(1/81a的8次方b的8次方)
=-72ab²

2、[(x+y)²-(x+y)(x-y)]÷2y
=(x+y)(x+y-x+y)÷2y
=2y(x+y)÷2y
=x+y1����֪:(x+y)²=16,(x-y)²=9,��xy��x²+y²��ֵ2����֪a+b=4,x+y=10,��a²+2ab+b²-x-y��ֵ�ǣ���Ҫ��̣�����ɺ�������лл��ȷ���ڶ�������Ķԣ���Ȼ�ǶԵ�