求數(shù)列的前N項(xiàng)和Sn的最大直
熱心網(wǎng)友
顯然s8最大證明Sn=[a1+a1+(n-1)d]*n/2 =[30-2n+2]*n/2 =16n-n^2 =-(n-8) ^2+64
熱心網(wǎng)友
An=a1+(n-1)d=15-(n-1)2≥0此時(shí)n≤8.5 最大取8Sn＝na1+(n-1)/2 .nd＝15n+[(n-1).nd]/2n=8Sn=176
熱心網(wǎng)友
An=15+(n-10)*-2
熱心網(wǎng)友
等差系數(shù)是-17/3數(shù)列的前N項(xiàng),好像寫(xiě)不完吧？前三項(xiàng)和最大是131/3