Create a graph of the sequence of triangular numbers (n) = n(n+1) / 2 , where n is a positive integer.

  see below for the graph

Step-by-step explanation:

For this sort of effort, it usually works well to use a spreadsheet or graphing calculator to graph the values in a table. Such a tool can create the table from the given formula.

a_n = a_1 + (n - 1)d

the first term is 6.

the common difference d = ?

when you find d, replace n with 7 and d with the common difference to find your answer.