The first term of arithmetic progression is a 1, the last term is an, the number of terms is n, the tolerance is d, and the sum of the first n terms is s n.

2, arithmetic progression's general formula:

The first term of arithmetic progression is a 1, the last term is an, the number of terms is n, the tolerance is d, and the sum of the first n terms is s n.

3. arithmetic progression's judgment:

4, the basic nature of arithmetic progression:

Knowledge points:

Arithmetic progression's basic formula:

The last term = the first term+(number of terms-1)× tolerance.

Number of items = (last item-first item) ÷ tolerance+1

The first item = the last item-(item number-1)× tolerance

Sum = (first item+last item) × number of items ÷2

The last item: the last digit

Item 1: the first digit

Number of items: How many digits does a * * * have?

Sum: Find the sum of a * * * number