¾ç¼ö ( a, b, c )¿¡ ´ëÇØ Ç¥Çö½Ä ( S = \frac{a}{b+c} + \frac{b}{a+c} + \frac{c}{a+b} )ÀÇ ÃÖ¼Ú°ªÀ» ã±â À§ÇØ ´ÙÀ½°ú °°Àº Á¢±ÙÀ» »ç¿ëÇÒ ¼ö ÀÖ½À´Ï´Ù.
´Ü°è 1: ´ëĪ¼º ÀǽÄÇϱâ
ÀÌ Ç¥Çö½ÄÀº ( a, b, c )¿¡ ´ëÇØ ´ëĪÀûÀÔ´Ï´Ù. µû¶ó¼ ( a = b = c )ÀÎ °æ¿ì¸¦ °í·ÁÇÏ¸é ºÒ¸®ÇÑ °æ¿ì°¡ ¾Æ´Ò °ÍÀÔ´Ï´Ù.
´Ü°è 2: µ¿µîÇÑ °ªÀ¸·Î ¼³Á¤
( a = b = c = k )¶ó°í °¡Á¤ÇØ º¾½Ã´Ù. ÀÌ °æ¿ì:
[
S = \frac{k}{k+k} + \frac{k}{k+k} + \frac{k}{k+k} = \frac{k}{2k} + \frac{k}{2k} + \frac{k}{2k} = \frac{1}{2} + \frac{1}{2} + \frac{1}{2} = \frac{3}{2}
]
´Ü°è 3: ºÒÆòµî Àû¿ëÇϱâ
Cauchy-Schwarz ºÎµî½ÄÀ» »ç¿ëÇÏ¿© ´ÙÀ½°ú °°ÀÌ Ç¥ÇöÇÒ ¼ö ÀÖ½À´Ï´Ù.
[
\left( \frac{a}{b+c} + \frac{b}{c+a} + \frac{c}{a+b} \right) \left( (b+c) + (c+a) + (a+b) \right) \geq (a+b+c)^2
]
¿©±â¼ ¾çº¯À» Á¤¸®Çϸé,
[
S \cdot 2(a+b+c) \geq (a+b+c)^2
]
À̸¦ ÅëÇØ ( S )¿¡ ´ëÇÑ ºÎµî½ÄÀ» ¾ò°Ô µË´Ï´Ù.
´Ü°è 4: ÃÖ¼Ú°ª ±¸Çϱâ
¾çº¯À» ( 2(a+b+c) )·Î ³ª´©¸é:
[
S \geq \frac{(a+b+c)^2}{2(a+b+c)} = \frac{a+b+c}{2}
]
µû¶ó¼, ( S )ÀÇ ÃÖ¼Ú°ªÀ» ã±â À§ÇØ ( a + b + c )¸¦ ÃÖ¼ÒÈÇØ¾ß ÇÕ´Ï´Ù. ( a, b, c )°¡ ¸ðµÎ °°À» ¶§, Áï ( a = b = c )ÀÏ ¶§ ÃÖ¼Ò°ªÀ» ±¸ÇÒ ¼ö ÀÖ½À´Ï´Ù.
[
S \geq \frac{3k}{2} \text{ (¿©±â¼ } k = a = b = c\text{)}
]
°á·Ð
µû¶ó¼, ( S )ÀÇ ÃÖ¼Ú°ªÀº ( \frac{3}{2} )ÀÔ´Ï´Ù. ÀÌ °ªÀº ( a = b = c )ÀÏ ¶§ ´Þ¼ºµË´Ï´Ù.
Áï,
[
S_{\text{min}} = \frac{3}{2}
]ÀÔ´Ï´Ù.