有關A4x2的精選大全

化簡、求值:已知A=4x2﹣4xy﹣y2,B=﹣x2+xy+7y2,①求﹣A﹣3B,②若A=﹣1,B=時,求6...
問題詳情:化簡、求值:已知A=4x2﹣4xy﹣y2,B=﹣x2+xy+7y2,①求﹣A﹣3B,②若A=﹣1,B=時,求6x2﹣6xy﹣15y2的值.【回答】解:①﹣A﹣3B=﹣(4x2﹣4xy﹣y2)﹣3(﹣x2+xy+7y2)=﹣4x2+4xy+y2+3x2﹣3xy﹣21y2=﹣x2+xy+y2﹣20y2②當A=﹣1,B=時,6x2﹣6xy﹣15y2=(4x2﹣4xy﹣y2)﹣2(﹣x2+xy+7y2)=A﹣2B=﹣1﹣1=﹣2知識...
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