先化简再求值:(a-2b)+2(a+b)(a-b)-3(a-2b)²,其中a=-2,b=1_数学解答

先化简再求值:(a-2b)+2(a+b)(a-b)-3(a-2b)²,其中a=-2,b=1

人气：112 ℃　时间：2019-12-20 08:23:40

解答

(a-2b)+2(a+b)(a-b)-3(a-2b)²=a-2b+2(a²-b²)-3(a²-4ab+4b²)=a-2b+2a²-2b²-3a²+12ab-12b²=-a²+12ab-14b²+a-2b=-4+12x(-2)x1-14+(-2)-2=-4-24-14-2-2=-46啊啊啊打错了是
a(a-2b)+2(a+b)(a-b)-3(a-2b)²a(a-2b)+2(a+b)(a-b)-3(a-2b)²

=a²-2ab+2(a²-b²)-3(a²-4ab+4b²)

=a²-2ab+2a²-2b²-3a²+12ab-12b²
=10ab-14b²
=10x(-2)x1-14
=-20-14
=-34