化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1

来源:学生作业帮助网 编辑:六六作业网 时间:2024/11/05 20:26:04
化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1化简求值

化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1
化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1

化简求值:(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b),a=-1,b=1
原式=(a³+2a²b+4ab²-2a²b-4ab²-8b³)-a(a²-2ab-15b²)
=a³-8b³-a³-2a²b+15ab²
=-8b³-2a²b+15ab²
=-8-2-15
=-25

解: (a-2b)(a²+2ab+4b²)-a(a-5b)(a+3b)
=a³-(2b)³-a(a²+3ab-5ab-15b²)
=a³-8b³-a³+2a²b+15ab²
=2a²b+15ab²-8b³
因为a=-1, b=1
则原式=2×(-1)²×1+15×(-1)×1²-8×1³
=2-15-8
=-21