已知2x减y的绝对值等于负七,3x的绝对值加2y等于0,求xy的值(过程要详细)
人气:416 ℃ 时间:2019-08-20 05:32:34
解答
2x-∣y∣= -7
y≥0时,2x-y= -7;y<0时,2x+y= -7
∣3x∣+2y=0
x≥0时,3x+2y= 0;x<0时,-3x+2y= 0
组成四个方程组:
(1)2x-y= -7,3x+2y= 0;得x= -2,y=3,xy= -6
(2)-3x+2y= 0,2x-y= -7;得x= -14,y= -21,xy=294
(3)2x+y= -7,3x+2y= 0;得x= -14,y=21,xy=-294
(4)-3x+2y= 0,2x+y= -7;得x=-2,y=-3,xy=6
综上:xy=±6或±294
或者:
2x-∣y∣= -7,∣y∣= 2x+7,y²=(2x+7)²,4y²=(4x+14)²,
∣3x∣+2y=0,4y²=(3x)²
4x+14=±3x,x=-2或-14,再代入4y²=(3x)²,y=±3或±21,可求出xy
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