满足an＋1=an＋3n＋2,且a1=2,求an
问题描述：
满足an＋1=an＋3n＋2,且a1=2,求an
答
an-an-1= 3(n-1)+2
an-1-an-2= 3(n-2)+2
...
a2-a1= 3+2
把以上式子相加 得
an-a1= 3(1+2+3+...+n-1)+2(n-1)
=3/2*n(n-1)+2(n-1)
=>an=3/2*n(n-1)+2(n-1) +2
=3/2*n(n-1)+2n