已知数列﹛an﹜满足an+1=an+n,﹙n+1)为下标,且a58=2007,则a1=

问题描述:

已知数列﹛an﹜满足an+1=an+n,﹙n+1)为下标,且a58=2007,则a1=

a58=a1+1+2+3+……+57=2007
a1+(1+57)×57÷2=2007
a1=354看不懂,a58=a1+1+2+3+……+57=2007a1+(1+57)×57÷2=2007什么意思,能详细点吗,谢谢an+1=an+na2=a1+1a3=a2+2=a1+1+2a4=a3+3=a1+1+2+3……………………an=an-1+n=a1+1+2+3+……+(n-1)a58=a1+1+2+3+……+57=20071+2+3+……+57=(1+57)×57÷2=1653a1=2007-1653=354