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数学
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设x²+xy=3,xy+y²=-2,则2x²-xy-3y²的值是多少?做这种题的方法是什么?
人气:468 ℃ 时间:2019-11-13 16:57:54
解答
2x²-xy-3y²
=2x²+2xy-3xy-3y²
=2(x²+xy)-3(xy+y²)
=2×3-3×(-2)
=6+6
=12
整体法
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