å·²ç¥å¤é¡¹å¼f(x)=a0+a1x+a2x^2+a3x^3+â¦â¦+a(n-1)x^(n-1)+anx^n
å
¶ä¸ï¼a0,a1,a2,â¦â¦,anæçå·®ï¼ä¸f(0)=f(1)=105ï¼f(-1)=15ï¼æ±nåançå¼ã
解æï¼âµf(x)=a0+a1x+a2x^2+a3x^3+â¦â¦+a(n-1)x^(n-1)+anx^n
å
¶ä¸ï¼a0,a1,a2,â¦â¦,anæçå·®ï¼ä¸f(0)=f(1)=105ï¼f(-1)=15
â´f(0)=a0=105ï¼f(1)=105+a1+a2+â¦+an=105
a0+(a0+d)+(a0+2d)+.....+(a0+nd)=105(n+1)+n(n+1)d/2=105
==>105n=-n(n+1)d/2
âµnâN*
â´(n+1)d=-210 (1)
å½n为å¥æ°æ¶ï¼f(-1)=(a0-a1)+(a2-a3)+....+[a(n-1)-an]=(n+1)d/2=15ï¼ä¸ï¼1ï¼çç¾ï¼æ以nä¸è½ä¸ºå¥æ°ã
â´n为å¶æ°
å³ï¼f(-1)=a0+(-a1+a2)+(-a3+a4)+.....+[-a(n-1)+an]
âµan-a(n-1)=a0+nd-a0-(n-1)d=d
â´f(-1)=a0+nd/2=105+nd/2=15 (2)
(1)(2)èç«è§£å¾n=6ï¼d=-30
an=-75
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å½nçäºå¥æ°æ¶ä¸ºä»ä¹ä¼çç¾å¢
追çåºè¯¥(n+1)d=-210ï¼è¥n为å¥æ°(n+1)d/2=15==>(n+1)d=30ï¼å³ä¸çäº-210