#1
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ÁÕäÁéÊÓËÃѺ¡Ò÷ÓÃÑéÇ 24 àÁµÃ ãªéäÁé·Ñé§ËÁ´¹ÕéÅéÍÁÃÑéǺÃÔàdzÃÙ»ÊÕèàËÅÕèÂÁÁØÁ©Ò¡ ãËé A = ¾×é¹·Õè¢Í§ºÃÔàdzÃÑéÇ ¨§ËÒ¤èҢͧ A ·ÕèÁÒ¡·ÕèÊØ´·Õèà»ç¹ä»ä´é¤×ÍÍÐäÃ
27 Á¡ÃÒ¤Á 2008 21:06 : ¢éͤÇÒÁ¹Õé¶Ù¡á¡éä¢áÅéÇ 1 ¤ÃÑé§, ¤ÃÑé§ÅèÒÊØ´â´Â¤Ø³ TOP à˵ؼÅ: Merge Post |
#2
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¼ÁÇèÒ 36 µÃ.Á. ÁÑꧤÃѺ
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µéͧà¢éÒã¨ãËéä´é äÁèÁÕã¤ÃÅÔ¢ÔµµÑÇàÃÒ ¹Í¡¨Ò¡µÑÇàÃÒ àÃÒà»ç¹¤¹àÅ×Í¡àͧ¤Ñº |
#3
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á¹Ç¤Ô´ ÊÃéÒ§ÊÁ¡Òèҡ⨷ÂìãËéä´é ÊÁ¡Ò÷ÕèÇèÒà»ç¹ÊÁ¡ÒÃ......
quardratic equation ËÃ×Í à»ç¹ÊÁ¡Òà ¾ÒÃÒâºÅèÒ «Ö觨ҡÊÁ¡ÒùÕé¨ÐÊÒÁÒöËҨشÊÙ§§ÊØ´ä´é $ x = - \frac{b}{2a}$ |
#4
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·Óâ´Âãªé¤ÇÒÁÃÙéà¡ÕèÂǡѺÍÊÁ¡Òáçä´é¤ÃѺ
ÊÁÁµÔÇèÒÃÑéÇ ¡ÇéÒ§ $x$ àÁµÃ ÂÒÇ $y$ àÁµÃ ¨Ðä´éÇèÒ $x+x+y+y=24\Rightarrow x+y=12$ ¾×é¹·ÕèÊÕèàËÅÕèÂÁ·Õèµéͧ¡Òä×Í $A=xy$ â´ÂÍÊÁ¡Òà AM-GM ¨Ðä´éÇèÒ $$A=xy\leq \frac{(x+y)^2}{4}=36$$ ÊÁ¡ÒÃà»ç¹¨ÃÔ§àÁ×èÍ $x=y=6$ ´Ñ§¹Ñé¹ ¾×é¹·ÕèÃÑéÇ·ÕèÁÒ¡·ÕèÊØ´¤×Í $36$ µÒÃÒ§àÁµÃ «Ö觷Óä´éâ´ÂÅéÍÁÃÑéÇãËéà»ç¹ÃÙ»ÊÕèàËÅÕèÂÁ¨ÑµØÃÑÊ·ÕèÁÕ¤ÇÒÁÂÒÇ´éÒ¹ $6$ àÁµÃ
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site:mathcenter.net ¤Ó¤é¹ |
#5
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¼Á¨Ðà¢Õ¹ÅÐàÍÕ´æ ãË餹·ÕèäÁèà¢éÒ㨴٤ÃѺ
¼Á¨Ðà¢Õ¹ÅÐàÍÕ´æ ãË餹·ÕèäÁèà¢éÒ㨴٤ÃѺ
$ãËé ´éҹ˹Ö觢ͧÃÙ»ÊÕèàËÅÕèÂÁ¡ÇéÒ§ x ˹èÇÂ(ÂÒÇà·èҡѺ´éÒ¹µÃ§¢éÒÁ)$ $áÅéÇÍÕ¡Êͧ´éÒ¹·ÕèàËÅ×ͨÐÂÒÇ \frac{24-2x}{2} ˹èÇÂ$ $ÊÁ¡ÒþÒÃÒâºÅÒ ¤×Í y=(12-x)x= -x^{2}+12x$ $¾×é¹·Õè ÁÒ¡·ÕèÊØ´¤×Í 36$ 28 Á¡ÃÒ¤Á 2008 17:29 : ¢éͤÇÒÁ¹Õé¶Ù¡á¡éä¢áÅéÇ 2 ¤ÃÑé§, ¤ÃÑé§ÅèÒÊØ´â´Â¤Ø³ ¹ÒÂʺÒ |
#6
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à©Å ¤ÓµÍº¤×Í 36 ¤ÃѺ
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#7
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¼ÁÅͧ·Óµèͨҡ¤Ø³ ¹ÒÂʺÒ ¹Ð¤ÃѺ
ÊÁ¡ÒþÒÃÒâºÅÒ¤×Í $y$ = $(12−x)x$ = $−x^2+12x$ $y$ = $−x^2$ + $12x$ = 36 -$−x^2$ + $2(6x)$ - $6^2$ = $36$ - $(x-6)^2$ $y_{max}$ = $36$ µÒÃÒ§àÁµÃ ÂѧÍÕ¡ÇÔ¸Õ $\frac{dy}{dx}$ = $-2x$ + $12$ = $0$ --> $x = 12/2 = 6 àÁµÃ$ $y_{max}$ = $36 µÃ.Á.$ |
#8
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¢éÍÊͺá¹Ç¹Õé¼ÁÁÑ¡ãªé
24=2¡ x 2 â´Âáºè§àÊé¹àª×Í¡ÍÍ¡à»ç¹2Êèǹ á·¹ 2¡=12 ¡=6 á·¹ 2Â=12 Â=6 áÅéÇàÍÒ¡ÇéÒ§¤Ù³ÂÒÇ 6x6=36 Áѹ§èÒ´ÕÍèФÃѺÊÓËÃѺ¢éÍÊͺ»Ã¹ÑÂ
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