已知xy=3,x2+xy-2y2=2(x+2y),且x≠-2y,则x+y=______.
题型:填空题难度:一般来源:不详
已知xy=3,x2+xy-2y2=2(x+2y),且x≠-2y,则x+y=______. |
答案
∵x2+xy-2y2=2(x+2y), ∴(x-y)(x+2y)=2(x+2y),即(x-y)(x+2y)-2(x+2y)=0, 分解因式得:(x+2y)(x-y-2)=0, 可得x+2y=0(舍去)或x-y-2=0, ∴x-y-2=0,即x-y=2, 又xy=3, ∴(x+y)2=(x-y)2+4xy=4+12=16, 则x+y=±4. 故答案为:±4 |
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