若a2+3ab=4,5ab+2b2=2,则2a2-9ab-6b2的值为
...字母后面的数字是次数
人气:237 ℃ 时间:2020-02-05 01:16:57
解答
2a2-9ab-6b2
=2a2+6ab-15ab-6b2
=(2a2+6ab)-(15ab+6b2)
=2(a2+3ab)-3(5ab+2b2)
=2×4-3×2
=8-6
=2
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