Question

已知xy＝-2，x+y＝4，求整式（4xy+11y）+[5x-（3xy+2y-4x）]的值。

Answer 1

解：去括号：
原式＝4xy+11y+5x-3xy-2y+4x
＝xy+9x+9y
＝xy+9（x+y）
已知xy＝-2，x+y＝4
则xy+9（x+y）＝-2+9x4
＝-2+36
＝34

Answer 2

(4xy+11y)+[5x-(3xy+2y-4x)]
=4xy+11y+(5x-3xy-2y+4x)
=4xy+11y+9x-3xy-2y
=xy+9y+9x
=xy+9(x+y)
=-2+9×4
=-2+36
=34

Answer 3

(4xy＋11y)＋〔5x－(3xy＋2y－4x)〕＝4xy＋11y＋5x－3xy－2y＋4x＝xy＋9(x＋y)
已知xy＝－2，x＋y＝4
原式＝－2＋9×4＝34

Answer 4

先化简，后整体代入计算，
化简原式=4xy+11y+5x-3xy-2y+4x
=xy+9x+8y
=xy+9（x+y）,
=-2+9×4=-2+36=34

Answer 5

xy=-2, x+y=4

(4xy+11y)+[5x-(3xy+2y-4x)]
=4xy+11y+5x-3xy-2y+4x
=xy+9(x+y)
=-2+9(6)
=-2+36
=34