作业帮(x+y+3)(x+y-3)=55,求x+y的值
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(x+y+3)(x+y-3)=55,求x+y的值
(x+y+3)(x+y-3)=55,求x+y的值
(x+y+3)(x+y-3)=55,求x+y的值
(x+y+3)(x+y-3)=55,求x+y的值
(x+y+3)(x+y-3)=55
(x+y)²-9=55
（x+y)²=64
∴x+y=±8
楼上的回答是错误的.
设x+y=t
则(t+3)(t-3)=55
t²-9=55
t²=64
解得t=8或-8
因为t=x²+y²≥0，所以t=-8＜0 舍去
故x+y=t=8
答案：x+y=8
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