已知(x+y)²=25,(x-y)²=9,求xy和x²+y²的值.但我绝不抄答案.→_→
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/04 06:32:17
![已知(x+y)²=25,(x-y)²=9,求xy和x²+y²的值.但我绝不抄答案.→_→](/uploads/image/z/2108137-49-7.jpg?t=%E5%B7%B2%E7%9F%A5%EF%BC%88x%EF%BC%8By%EF%BC%89%26%23178%3B%EF%BC%9D25%2C%EF%BC%88x%EF%BC%8Dy%EF%BC%89%26%23178%3B%EF%BC%9D9%2C%E6%B1%82xy%E5%92%8Cx%26%23178%3B%EF%BC%8By%26%23178%3B%E7%9A%84%E5%80%BC.%E4%BD%86%E6%88%91%E7%BB%9D%E4%B8%8D%E6%8A%84%E7%AD%94%E6%A1%88.%E2%86%92_%E2%86%92)
已知(x+y)²=25,(x-y)²=9,求xy和x²+y²的值.但我绝不抄答案.→_→
已知(x+y)²=25,(x-y)²=9,求xy和x²+y²的值.
但我绝不抄答案.→_→
已知(x+y)²=25,(x-y)²=9,求xy和x²+y²的值.但我绝不抄答案.→_→
∵(x+y)²=25
(x-y)²=9
∴xy=[(x+y)²-(x-y)²]/4
=(25-9)/4
=16/4
=4
∴x²+y²
=(x+y)²-2xy
=25-2×4
=25-8
=17