Exercise 2 Page 199

In an arithmetic sequence, you can find each new term by always adding (or subtracting) the same number to the previous term. The number that is added or subtracted each time is called the common difference of the sequence. Therefore, a pattern that increases or decreases by the same amount each time can be described by an arithmetic sequence.

Example

A small cinema has $25$ rows of seats and the first row has $18$ seats. Each row has two more seats than the previous row. The number of seats in each row, from the first to the last, can be written as an arithmetic sequence.