ijÔì´¬¹«Ë¾Äê×î¸ßÔì´¬Á¿ÊÇ20ËÒ. ÒÑÖªÔì´¬xËҵIJúÖµº¯ÊýR (x)=3700x + 45x2 ¨C 10x3(µ¥Î»£ºÍòÔª), ³É±¾º¯ÊýΪC (x) = 460x + 5000 (µ¥Î»£ºÍòÔª). ÓÖÔÚ¾­¼ÃѧÖУ¬º¯Êýf(x)µÄ±ß¼Êº¯ÊýMf (x)¶¨ÒåΪ: Mf (x) = f (x+1) ¨C f (x). Çó:£¨Ìáʾ£ºÀûÈó = ²úÖµ ¨C ³É±¾£©

(1) ÀûÈóº¯ÊýP(x) ¼°±ß¼ÊÀûÈóº¯ÊýMP(x);

    (2) ÄêÔì´¬Á¿°²ÅŶàÉÙËÒʱ, ¿Éʹ¹«Ë¾Ôì´¬µÄÄêÀûÈó×î´ó?

    (3) ±ß¼ÊÀûÈóº¯ÊýMP(x)µÄµ¥µ÷µÝ¼õÇø¼ä, ²¢ËµÃ÷µ¥µ÷µÝ¼õÔÚ±¾ÌâÖеÄʵ¼ÊÒâÒåÊÇʲô£¿

(1) P(x) =  ¨C 10x3 + 45x2 + 3240x ¨C 5000  (x??NÇÒx??[1, 20]);  

  MP (x) = ¨C 30x2 + 60x +3275   (x??NÇÒx??[1, 20]). 

 (2)Ä꽨Ôì12ËÒ´¬Ê±, ¹«Ë¾Ôì´¬µÄÄêÀûÈó×î´ó.                      

 (3)µ±1< x ?? 20ʱ£¬MP (x)µ¥µ÷µÝ¼õ.                              

 MP (x)ÊǼõº¯Êý˵Ã÷: Ëæ×ŲúÁ¿µÄÔö¼Ó£¬Ã¿ËÒÀûÈóÓëǰһ̨±È½Ï£¬ÀûÈóÔÚ¼õÉÙ.1


½âÎö:

(1) P(x) = R (x) ¨C C (x) = ¨C 10x3 + 45x2 + 3240x ¨C 5000  (x??NÇÒx??[1, 20]);   2·Ö

  MP (x) = P ( x + 1 ) ¨C P (x) = ¨C 30x2 + 60x +3275   (x??NÇÒx??[1, 20]). 

 (2) P`(x) = ¨C 30x2 + 90x + 3240 = ¨C 30( x +9 )(x ¨C 12)  (x??NÇÒx??[1, 20])

       µ±1< x < 12ʱ, P`(x) > 0, P(x)µ¥µ÷µÝÔö,

       µ± 12 <x < 20ʱ, P`(x) < 0 , P ( x ) µ¥µ÷µÝ¼õ.

    ¡à x = 12 ʱ, P(x)È¡×î´óÖµ,                                       

¼´, Ä꽨Ôì12ËÒ´¬Ê±, ¹«Ë¾Ôì´¬µÄÄêÀûÈó×î´ó.                      

 (3) ÓÉMP(x ) =  ¨C 30( x ¨C 1) 2 + 3305   (x??NÇÒx??[1, 20]).

    ¡àµ±1< x ?? 20ʱ£¬MP (x)µ¥µ÷µÝ¼õ.                                 12·Ö

 MP (x)ÊǼõº¯Êý˵Ã÷: Ëæ×ŲúÁ¿µÄÔö¼Ó£¬Ã¿ËÒÀûÈóÓëǰһ̨±È½Ï£¬ÀûÈóÔÚ¼õÉÙ.1

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