已知x+y=6,xy=-5,则x-y的值是
问题描述：
已知x+y=6,xy=-5,则x-y的值是
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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