(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b)其中a=-1,b=1(先化简,再求值)

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(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b)其中a=-1,b=1(先化简,再求值)
(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b)
其中a=-1,b=1(先化简,再求值)

(a-2b)(a^2+2ab+4b^2)-a(a-5b)(a+3b)其中a=-1,b=1(先化简,再求值)
(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

=(a+b-3b)[(a+b)^2+3b^2]-a(a+b-6b)(a+b+2b)
=(-3b)(3b^2)-a(-6b)(2b)
=-9b^3+6ab^2
=-9-6
=-15