已知|x|=5,y2=4,且x+y＜0，则xy的值等于（）（A）10或-10

已知|x|=5,y2=4,且x+y＜0，则xy的值等于（）

（A）10或-10 （B）10 （C）-10 （D）以上答案都不对

答案

A.因为|x|=5,y2=4,所以x=±5,y=±2.又因为x+y＜0，所以x=-5,y=2或x=-5,y=-2，因此xy=(-5)×2=-10或xy=(-5)×(-2)=10.

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已知|x|=5,y2=4,且x+y＜0，则xy的值等于（ ） （A）10或-10

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已知|x|=5,y2=4,且x+y＜0，则xy的值等于（）（A）10或-10