Lesson Summary: By the end of this lesson, one should be familiar with d- the common difference of a sequence of numbers which can be found by subtracting a term by its previous term in the sequence which should equal a constant u sub n - u sub n-1 = d. Furthermore,  one should know the explicit formula a sub n is = a sub 1 + (n-1) d. In addition, one should know that the explicit formula of an arithmetic sequence is linear, and to find the sum of an arithmetic sequence, one should utilize S sub n = n/2 (u sub 1 + u sub n).