Sum formula calculation is accumulation. The addition of the latter term and the former term can save part of the accumulation method, and the multiplication of the latter term and the former term can save part of the accumulation method. Generally speaking, the general term formula and sum can be derived by accumulation method, but only the general term formula can be derived by accumulation method, that is, the recurrence relation a(n+ 1)-an=f(n), and the recurrence relation between an accumulation method and an accumulation method can be found.

Cumulative symbols refer to

The symbol of accumulation is the capital of the Greek letter σ, which usually means addition in mathematics. The lowercase σ represents the difference between area density and packing density and linear density. For the cumulative sum of functions, n takes a continuous integer value of M and K, and this variable N can be changed into any other letter, such as X. We call the following N equal to M, and the above K is the subscript of this sum. If the context is clear, the subscript can be omitted. Sum symbols can also represent infinite series.