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ij³§Éú²úijÖÖ²úÆ·µÄÄê¹Ì¶¨³É±¾Îª250ÍòÔª,ÿÉú²úxǧ¼þ,ÐèÁíͶÈë³É±¾ÎªC(x),µ±Äê²úÁ¿²»×ã80ǧ¼þʱ,C(x)=x2+10x(ÍòÔª).µ±Äê²úÁ¿²»Ð¡ÓÚ80ǧ¼þʱ,C(x)=51x+-1450(ÍòÔª).ÿ¼þÉÌÆ·ÊÛ¼ÛΪ0.05ÍòÔª.ͨ¹ýÊг¡·ÖÎö,¸Ã³§Éú²úµÄÉÌÆ·ÄÜÈ«²¿ÊÛÍê.
(1)д³öÄêÀûÈóL(x)(ÍòÔª)¹ØÓÚÄê²úÁ¿x(ǧ¼þ)µÄº¯Êý½âÎöʽ.
(2)Äê²úÁ¿Îª¶àÉÙǧ¼þʱ,¸Ã³§ÔÚÕâÒ»ÉÌÆ·µÄÉú²úÖÐËù»ñÀûÈó×î´ó?
(1) L(x)=
(2) µ±²úÁ¿Îª100ǧ¼þʱ,¸Ã³§ÔÚÕâÒ»ÉÌÆ·µÄÉú²úÖÐËù»ñÀûÈó×î´ó,×î´óÀûÈóΪ1000ÍòÔª.
(1)ÒòΪÿ¼þÉÌÆ·ÊÛ¼ÛΪ0.05ÍòÔª,Ôòxǧ¼þÉÌÆ·ÏúÊÛ¶îΪ0.05¡Á1000xÍòÔª,ÒÀÌâÒâµÃ:µ±0<x<80ʱ,L(x)=(0.05¡Á1000x)-x2-10x-250=
-x2+40x-250.
µ±x¡Ý80ʱ,L(x)=(0.05¡Á1000x)-51x-+1450-250=1200-(x+).
ËùÒÔL(x)=
(2)µ±0<x<80ʱ,L(x)=-(x-60)2+950.
´Ëʱ,µ±x=60ʱ,L(x)È¡µÃ×î´óÖµ,L(60)=950ÍòÔª.
µ±x¡Ý80ʱ,L(x)=1200-(x+)¡Ü1200-2=1200-200=1000,
´Ëʱ,µ±x=ʱ,¼´x=100ʱ,L(x)È¡µÃ×î´óÖµ1000ÍòÔª.
¡ß950<1000,
ËùÒÔ,µ±²úÁ¿Îª100ǧ¼þʱ,¸Ã³§ÔÚÕâÒ»ÉÌÆ·µÄÉú²úÖÐËù»ñÀûÈó×î´ó,×î´óÀûÈóΪ1000ÍòÔª.
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