已知x+y=-5,xy=3,则x²+y²的值是19.为啥~还有一道.差不多的若x+y=3,xy=1,求x²+y²的值
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![已知x+y=-5,xy=3,则x²+y²的值是19.为啥~还有一道.差不多的若x+y=3,xy=1,求x²+y²的值](/uploads/image/z/4074279-15-9.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D-5%2Cxy%3D3%2C%E5%88%99x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC%E6%98%AF19.%E4%B8%BA%E5%95%A5%7E%E8%BF%98%E6%9C%89%E4%B8%80%E9%81%93.%E5%B7%AE%E4%B8%8D%E5%A4%9A%E7%9A%84%E8%8B%A5x%2By%3D3%2Cxy%3D1%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%E7%9A%84%E5%80%BC)
已知x+y=-5,xy=3,则x²+y²的值是19.为啥~还有一道.差不多的若x+y=3,xy=1,求x²+y²的值
已知x+y=-5,xy=3,则x²+y²的值是19.为啥~
还有一道.差不多的
若x+y=3,xy=1,求x²+y²的值
已知x+y=-5,xy=3,则x²+y²的值是19.为啥~还有一道.差不多的若x+y=3,xy=1,求x²+y²的值
若x+y=-5,xy=3
则x²+y²
=x²+y²+2xy-2xy
=(x+y)²-2xy
=(-5)²-2*3
=19
同理:若x+y=3,xy=1,
则x²+y²=(x+y)²-2xy=3²-2*1=7
x+y=-5,xy=3,则x²+y²=(x+y)^2 =x^2 + y^2 + 2xy = 2
=>x^2 + y^2 = 25 - 2xy = 25 - 6 =19
x+y=3,xy=1,求x²+y²
(x+y)^2 = 9
x^2 +y^2 + 2xy = 9
=> x^2 + y^2 = 9 - 2 = 7
(x+y)²=9
x²+2xy+y²=9
2xy=2
所以x²+y²=9-2=7
x²+y²=(x+y)²-2xy=3²-2=7