先化简在求值(a-2b)(a²+2ab+4b²)-a(a-5b)(a+3b),其中a=-1,b=2
问题描述:
先化简在求值(a-2b)(a²+2ab+4b²)-a(a-5b)(a+3b),其中a=-1,b=2
答
(a-2b)(a²+2ab+4b²)-a(a-5b)(a+3b)=(a-2b)(a²+2ab+4b²)-a(a²-2ab-15b²)=a³+2a²b+4ab²-2a²b-4ab²-8b³-a³+2a²b+15ab²=2a²b+15ab...