已知x+y=3,xy=-7.求(x-y)^2的值

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已知x+y=3,xy=-7.求(x-y)^2的值
已知x+y=3,xy=-7.求(x-y)^2的值

已知x+y=3,xy=-7.求(x-y)^2的值
(x-y)^2
=x²-2xy+y²
=x²+2xy+y²-4xy
=(x+y)²-4xy
=3²-4×(-7)
=37

(x-y)^2
=x²-2xy+y²
=x²+2xy+y²-4xy
=(x+y)²-4xy
=9+28
=37

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