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å°åç沿çå¹³è¡äºæªé¢æ¹ååæn份ï¼nè¶åäºæ 穷大,å¾å°åå¾ä¸ä¸ï¼é«h=R/nçè¶
èåçï¼è¿äºåçå¯ä»¥è¿ä¼¼ä¸ºåæ±ä½ï¼ä»æªé¢å¾é¡¶ç«¯æ°ï¼ç¬¬1个åæ±ä½çåå¾r1ï¼ç±å¾è¡å®ç(r1)2=R2-(R/n)2(å 为表达å¼ä¸å¥½åï¼(r1)=åå¾r1çå¹³æ¹ï¼R2=Rçå¹³æ¹ï¼ãä½ç§¯V1=Ï(r1)2h第2个åæ±ä½åå¾(r2)2=R2-(2R/n)2 ,ä½ç§¯V2=Ï(r2)2hâ¦â¦ç¬¬n个åæ±ä½åå¾(rn)2=R2-(nR/n)2.ä½ç§¯Vn=Ï(rn)2h计ç®è¿n个åæ±ä½ä½ç§¯ä¹åå³ä¸ºåçä½ç§¯C
C=V1+V2+V3+â¦â¦+Vn=Ïh((r1)2+(r2)2+(r1)2+(r3)2+â¦â¦+(rn)2ï¼
=Ï*R/n*((R2-(R/n)2)+(R2-(2R/n)2)+(R2-(3R/n)2)+â¦â¦+(R2-(nR/n)2))
=Ï*R/n*(nR2-R2/n2-4R2/n2-9R2/n2-â¦â¦-n2R2/n2)
=Ï*R/n*R2*(n-1/n2-4/n2-9/n2-n2/n2)
=Ï*R3/n*(n-(1/n2)*(1+4+9+â¦â¦+n2) è¿éåç¨å¹³æ¹åå
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=Ï*R3/n*(n-(1/n2)*n*(n+1)(2n+1)/6
=Ï*R3*(n-n*(n+1)(2n+1)/(6n3)
=Ï*R3*(1-(n+1)(2n+1)/(6n2) åååæ¯çº¦å»n
=Ï*R3*(6n2-(2n2+3n+1))/(6n2)
=Ï*R3*(4n2-3n-1))/(6n2)
=Ï*R3*(4-3/n-1/n2)/6 åååæ¯çº¦å»n2
ç±äºnè¶åäºæ 穷大ï¼æ以3/nè¶åäº0,1/n2è¶åäº0
åçä½ç§¯C=Ï*R3*4/6=2/3*Ï*R3
V=2C=4/3*Ï*R3
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