若实数x,y满足x·x+xy+y=14,y·y+xy+x=28.则x+y的值等于
2个回答
两式相加,得
(x²+2xy+y²)+(x+y)-42=0
即(x+y)²+(x+y)-42=0
所以[(x+y)+7][(x+y)-6]=0
所以x+y=-7或x+y=6
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