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数学
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X2+Y2+XY=2,求X2+Y2-XY取值范围
人气:177 ℃ 时间:2020-01-29 06:37:25
解答
x^2+xy+y^2=2 ≥3xy
xy ≤2/3
-2xy≥-4/3,
x^2-xy+y^2=x^2+xy+y^2-2xy=2-2xy≥2/3
当且仅当 x=y时取等号>=2/3且<=6,我做出来。
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