已知数列{an}满足a1=2,an-an-1=3n,求an
问题描述:
已知数列{an}满足a1=2,an-an-1=3n,求an
答
累加法.an=(an-an-1)+(an-1 - an-2)+·······+(a2-a1)+a1=3n+3(n-1)+······+3*2+2=3(2+3+·····+n)+2=(3n^2+3n-2)/2
已知数列{an}满足a1=2,an-an-1=3n,求an
累加法.an=(an-an-1)+(an-1 - an-2)+·······+(a2-a1)+a1=3n+3(n-1)+······+3*2+2=3(2+3+·····+n)+2=(3n^2+3n-2)/2