等差数列{an}的前三项为:x-1,x+1,2x+3:则an等于?
问题描述:
等差数列{an}的前三项为:x-1,x+1,2x+3:则an等于?
答
an=2n-3
x+1-(x-1)=2x+3-(x+1)
x=0 d=2
an=-1+(n-1)x2
=2n-3