1+2+3+4+.+99ç¨ç®ä¾¿æ¹æ³
=ï¼1+99ï¼+ï¼2+98ï¼+...+ï¼49+51ï¼+50
=50*2*49+50
=50*(100-1)
=5000-50
=4950
æ¯çå·®æ°åçæ±åï¼å¯ä»¥ç´æ¥æ±ä¸é´çå¹³åå¼ï¼ç¶åä¹ä»¥æ»çæ°éè¿è¡è®¡ç®ã
å¦æä¸ä¸ªæ°åä»ç¬¬äºé¡¹èµ·ï¼æ¯ä¸é¡¹ä¸å®çåä¸é¡¹çå·®çäºåä¸ä¸ªå¸¸æ°ï¼è¿ä¸ªæ°åå°±å«åçå·®æ°åï¼è¿ä¸ªå¸¸æ°å«åçå·®æ°åçå ¬å·®ï¼å ¬å·®å¸¸ç¨åæ¯d表示ãçå·®æ°åæ¯å¸¸è§æ°åçä¸ç§ã
çå·®ä¸é¡¹å³çå·®æ°å头尾两项çåçä¸å.ä½æ±çå·®ä¸é¡¹ä¸ä¸å®è¦ç¥é头尾两项ã