(x+y)²=1,(x-y)²=11,求x+y与xy的值

(x+y)²=1,(x-y)²=11,求x+y与xy的值
(x+y)²=1,(x-y)²=11,求x+y与xy的值

(x+y)²=1,(x-y)²=11,求x+y与xy的值
问题：(x+y)²=1,(x-y)²=11,求x+y与xy的值.
　　解析：(x+y)²=1,x²+2xy+y²=1
(x-y)²=11,x²-2xy+y²=11
两式相减：4xy=-10,得xy=-5/2
(x+y)²=1,开方得：x+y=1或-1