Let's visualize the information we have been given. We notice that the numbers are getting lower, so the common difference has to be a negative number.
28 →+d 20 →+d 12 →+d 4
The of the arithmetic sequence can be determined by subtracting one of the terms from the next. Let's subtract the first term from the second term.
a2−a1=20−28=-8
Knowing the common difference, we should subtract
8 from
28 enough times until we end up at
-36. If we call this number of times
n, we get the following equation.
28−8n=-36
Let's solve for
n.
28−8n=-36 -8n=-64
The eight term is
-36.