a-b=3,ab-3,则3a-3b-6ab=
问题描述：
a-b=3,ab-3,则3a-3b-6ab=
答
3(a-b)-6ab
=3×3-6×3
=9-18
=-9
答
3a-3b-6ab=9+18=27
答
3a-3b-6ab
=3(a-b)-6ab
=3×3-6×(-3)
=27