已知xy=3,x+y=7,试求 (1)x方+xy+y方的值 (2)(x-y)方的值
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![已知xy=3,x+y=7,试求 (1)x方+xy+y方的值 (2)(x-y)方的值](/uploads/image/z/1652730-42-0.jpg?t=%E5%B7%B2%E7%9F%A5xy%3D3%2Cx%2By%3D7%2C%E8%AF%95%E6%B1%82+%EF%BC%881%EF%BC%89x%E6%96%B9%2Bxy%2By%E6%96%B9%E7%9A%84%E5%80%BC+%EF%BC%882%EF%BC%89%EF%BC%88x-y%29%E6%96%B9%E7%9A%84%E5%80%BC)
已知xy=3,x+y=7,试求 (1)x方+xy+y方的值 (2)(x-y)方的值
已知xy=3,x+y=7,试求 (1)x方+xy+y方的值 (2)(x-y)方的值
已知xy=3,x+y=7,试求 (1)x方+xy+y方的值 (2)(x-y)方的值
1、
(x+y)²=7²
x²+2xy+y²=49
xy=3
两边减去xy
x²+xy+y²=49-3=46
2、
(x-y)²
=x²-2xy+y²
=(x²+xy+y²)-3xy
=46-3×3
=37