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已知x+y=6,xy=-5,则x-y的值是
人气:397 ℃ 时间:2020-02-03 06:14:20
解答
∵(x-y)²
=x²-2xy+y²
=(x²+2xy+y²)-4xy
=(x+y)²-4xy
=6²-4×(-5)
=36+20
=56
∴x-y=±2√14
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