已知x+y=7,x-y=5,求x2-y2-2y+2x的值.
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已知x+y=7,x-y=5,求x2-y2-2y+2x的值.
![已知x+y=7,x-y=5,求x2-y2-2y+2x的值.](/uploads/image/z/5961676-4-6.jpg?t=%E5%B7%B2%E7%9F%A5x%2By%3D7%EF%BC%8Cx-y%3D5%EF%BC%8C%E6%B1%82x2-y2-2y%2B2x%E7%9A%84%E5%80%BC%EF%BC%8E)
x2-y2-2y+2x
=(x+y)(x-y)-2(y-x)
=(x+y)(x-y)+2(x-y)
=(x-y)(x+y+2),
将x+y=7,x-y=5,代入上式得:
原式=(x-y)(x+y+2)=5×9=45.
=(x+y)(x-y)-2(y-x)
=(x+y)(x-y)+2(x-y)
=(x-y)(x+y+2),
将x+y=7,x-y=5,代入上式得:
原式=(x-y)(x+y+2)=5×9=45.
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