一道数学题,感觉好难啊!
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一道数学题,感觉好难啊!
已知X2+Y2=4 求2XY/X+Y+2的最小值
X2和Y2的2为平方..2XY/(X+Y+2)谢谢
已知X2+Y2=4 求2XY/X+Y+2的最小值
X2和Y2的2为平方..2XY/(X+Y+2)谢谢
![一道数学题,感觉好难啊!](/uploads/image/z/19893848-32-8.jpg?t=%E4%B8%80%E9%81%93%E6%95%B0%E5%AD%A6%E9%A2%98%2C%E6%84%9F%E8%A7%89%E5%A5%BD%E9%9A%BE%E5%95%8A%21)
已知x²+y²=4,求2xy/(x+y-2)的最小值.
由于(x-y)²≥0,展开得:2xy≤x²+y²,则有:
x²+y²+2xy≤2(x²+y²)
(x+y)²≤2(x²+y²)=8
得:-2√2≤x+y≤2√2,
所以有:
2xy/(x+y-2)
=(x²+y²+2xy-4)/(x+y-2)
=[(x+y)²-4]/(x+y-2)
=(x+y+2)(x+y-2)/(x+y-2)
=x+y+2≥2-2√2
因此,2xy/(x+y-2)的最小值是2-2√2.
由于(x-y)²≥0,展开得:2xy≤x²+y²,则有:
x²+y²+2xy≤2(x²+y²)
(x+y)²≤2(x²+y²)=8
得:-2√2≤x+y≤2√2,
所以有:
2xy/(x+y-2)
=(x²+y²+2xy-4)/(x+y-2)
=[(x+y)²-4]/(x+y-2)
=(x+y+2)(x+y-2)/(x+y-2)
=x+y+2≥2-2√2
因此,2xy/(x+y-2)的最小值是2-2√2.