x+y=m xy=n,求(x-y)²和x²+y²
问题描述:
x+y=m xy=n,求(x-y)²和x²+y²
答
解: x+y=m xy=n
(x-y)²
=(x+y)²-4xy
=m²-4n
x²+y²
=(x+y)²-2xy
=m²-2n
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