已知x+y=7,xy=12,求x²+y²的值 已知x-y=7,xy=12,求x²+y²的值
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![已知x+y=7,xy=12,求x²+y²的值 已知x-y=7,xy=12,求x²+y²的值](/uploads/image/z/2108205-45-5.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D7%2Cxy%3D12%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC+%E5%B7%B2%E7%9F%A5x-y%3D7%2Cxy%3D12%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC)
已知x+y=7,xy=12,求x²+y²的值 已知x-y=7,xy=12,求x²+y²的值
已知x+y=7,xy=12,求x²+y²的值 已知x-y=7,xy=12,求x²+y²的值
已知x+y=7,xy=12,求x²+y²的值 已知x-y=7,xy=12,求x²+y²的值
(x+y)²=x²+y²+2xy
49=x²+y²+2*12
即:x²+y²=25
x^2+y^2
=(x+y)^2-2xy
=7^2-2x12
=25
x^2+y^2
=(x-y)^2+2xy
=7^2+2x12
=73
完了,我不会,天啦!肿么会这个样子。