2.已知x+y=3,xy=2,求x²+y²的值 3.已知x-y=5,x²+y²=15,求xy的值2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知(a+b)²=17,ab=3.求(a-b)²的值
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![2.已知x+y=3,xy=2,求x²+y²的值 3.已知x-y=5,x²+y²=15,求xy的值2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知(a+b)²=17,ab=3.求(a-b)²的值](/uploads/image/z/4518021-21-1.jpg?t=2.%E5%B7%B2%E7%9F%A5x%2By%3D3%2Cxy%3D2%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC+3.%E5%B7%B2%E7%9F%A5x-y%3D5%2Cx%26%23178%3B%2By%26%23178%3B%3D15%2C%E6%B1%82xy%E7%9A%84%E5%80%BC2.%E5%B7%B2%E7%9F%A5x%2By%3D3%2Cxy%3D2%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC3.%E5%B7%B2%E7%9F%A5x-y%3D5%2Cx%26%23178%3B%2By%26%23178%3B%3D15%2C%E6%B1%82xy%E7%9A%84%E5%80%BC4.%E5%B7%B2%E7%9F%A5%EF%BC%88a%2Bb%EF%BC%89%26%23178%3B%3D17%2Cab%3D3.%E6%B1%82%EF%BC%88a-b%EF%BC%89%26%23178%3B%E7%9A%84%E5%80%BC)
2.已知x+y=3,xy=2,求x²+y²的值 3.已知x-y=5,x²+y²=15,求xy的值2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知(a+b)²=17,ab=3.求(a-b)²的值
2.已知x+y=3,xy=2,求x²+y²的值 3.已知x-y=5,x²+y²=15,求xy的值
2.已知x+y=3,xy=2,求x²+y²的值
3.已知x-y=5,x²+y²=15,求xy的值
4.已知(a+b)²=17,ab=3.求(a-b)²的值
2.已知x+y=3,xy=2,求x²+y²的值 3.已知x-y=5,x²+y²=15,求xy的值2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知(a+b)²=17,ab=3.求(a-b)²的值
2) x平方+y平方
=(x+y)平方-2xy
=9-4=5
3) x-y=5
∴x平方-2xy+y平方=25
∵x平方+y平方=15
∴15-2xy=25
∴xy=-5
4)(a-b)平方
=a平方-2ab+b平方
=(a+b)平方-4ab
=17-12=5