已知 a²-2ab=3,b²-ab=4,那么2b²-a²的值是多少?快些,thank you.
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已知 a²-2ab=3,b²-ab=4,那么2b²-a²的值是多少?快些,thank you.
已知 a²-2ab=3,b²-ab=4,那么2b²-a²的值是多少?
快些,thank you.
已知 a²-2ab=3,b²-ab=4,那么2b²-a²的值是多少?快些,thank you.
2(b²-ab)-( a²-2ab)
=2b²-a²
=2*4-3
=5
2b^2-a^2=2*(b^2-ab)-(a^2-2ab)
=2*(4)-3
=8-3
=5
由b²-ab=4得
2b²-2ab=8,2ab=2b²-8
∴ a²-2ab=a²-2b²+8=3
∴2b²-a²=8-3=5