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ËÒ n ¾¨¹ìáá¢Í§Í¹Ø¡ÃÁ 1+ 2+3+4 +3+4+5+6+7 +... ¢Íá¹Ç¤Ô´´éǤÃѺ¢Íº¤Ø³¤ÃѺ
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ÍéÒ§ÍÔ§:
$$ S_n= \sum_{i=1}^n (i+(i+1)+\dots +(3i-2)) $$ |
Âѧ§§ ÍÂÙèàŤÃѺ ¶éÒ¼Áá·¹ n=3 áÅéÇ áÅéǼźǡ n ¾¨¹ìáá ¨Ðà¢Õ¹ÍÂèÒ§ääÃѺ ªèÇ·ӵèÍãËéÍÕ¡ 1 ºÃ÷Ѵ¹Ð¤ÃѺ ¢Íº¤Ø³¤ÃѺ
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à·ÍÁ·ÕèÍÂÙèã¹ sigma à»ç¹Í¹Ø¡ÃÁàÅ¢¤³Ôµ ·Õèà¾ÔèÁ·ÕÅÐ 1 áÅкǡ¡Ñ¹ 2i-1 à·ÍÁ¤ÃѺ
´Ñ§¹Ñé¹ $$ S_n = \sum_{i=1}^n \,\, \big(\frac{2i-1}{2}\cdot(i+(3i-2)) \big) = \sum_{i=1}^n \,\, (2i-1)^2 $$ ¨Ò¡¹Ñé¹ ¶éÒ¡ÃШÒÂáÅéÇ take sigma ·éÒ·ÕèÊØ´ ¨ÐµÍº $ \frac{n(4n^2-1)}{3}$ ¤ÃѺ |
$a_1=1$
$a_2=2+3+4$ $a_3=3+4+5+6+7$ $a_4=4+5+6+7+8+9+10$ .... $a_n=n+(n+1)+(n+2)+...+(3n-2)=(2n-1)^2$ ËÒ $a_n$ ¨Ò¡Êٵà $\frac{n}{2}(a_1+a_n)$ ¼ÅºÇ¡ n ¾¨¹ìáá¢Í§Í¹Ø¡ÃÁàÅ¢¤³Ôµ ´Ñ§¹Ñé¹ $S_n=\sum_{i=1}^{n}a_n=\sum_{i=1}^{n}(2n-1)^2$ |
àÇÅÒ·ÕèáÊ´§·Ñé§ËÁ´ à»ç¹àÇÅÒ·Õè»ÃÐà·Èä·Â (GMT +7) ¢³Ð¹Õéà»ç¹àÇÅÒ 15:23 |
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