作业帮设A=a²+ab+b²,B=2a²-ab+2b²,当a=-1/3,b=-2时,求代数式2A-[(2A-B)-2(A-B)]的值.
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设A=a²+ab+b²,B=2a²-ab+2b²,当a=-1/3,b=-2时,求代数式2A-[(2A-B)-2(A-B)]的值.
设A=a²+ab+b²,B=2a²-ab+2b²,当a=-1/3,b=-2时,求代数式2A-[(2A-B)-2(A-B)]的值.
设A=a²+ab+b²,B=2a²-ab+2b²,当a=-1/3,b=-2时,求代数式2A-[(2A-B)-2(A-B)]的值.
原式=2A-[2A-B-2A+2B]
=2A-B
=2(a²+ab+b²)-(2a²-ab+2b²)
=2a²+2ab+2b²-2a²+ab-2b²
=3ab
当a=-1/3,b=-2时,
原式=3×(-1/3)×(-2)
=2