已知A=5a2-2ab+6,B=7ab-8a2-7,则A-2B=______.

问题描述:

已知A=5a2-2ab+6,B=7ab-8a2-7,则A-2B=______.

∵A=5a2-2ab+6,B=7ab-8a2-7,
∴A-2B=(5a2-2ab+6)-2(7ab-8a2-7)
=5a2-2ab+6-14ab+16a2+14
=21a2-16ab+20.
故答案为:21a2-16ab+20.
答案解析:直接把A=5a2-2ab+6,B=7ab-8a2-7代入A-2B进行计算即可.
考试点:整式的加减.


知识点:本题考查的是整式的加减,熟知整式的加减实质上是合并同类项是解答此题的关键.