Current location - Training Enrollment Network - Mathematics courses - The college entrance examination question in 2004 is the fifteenth question in mathematics (science)
The college entrance examination question in 2004 is the fifteenth question in mathematics (science)
An-1= a1+2a2+3a3+...+(n-2) an-22 formula

An = a 1+2a2+3a3+...+(n- 1) an- 1。

1 minus 2

An-an-1= (n-1) an-1,which means An=nAn- 1.

A2=(2- 1)A 1

This part is brought in directly. Note that the original title is n & gt=2, and if you accidentally A2=A 1+2A2, there will be a negative sign.

a2 = a 1 = 1 th EN A3 = a 1+2 a2 = 3

The general formula of branch one {An} is n! /2