In: Advanced Math
How many terms are in the finite arithmetic sequence 12, 20, 28, … , 172?
Consider the finite arithmetic sequence,
12, 20, 28, … 172
Use the explicit formula for an arithmetic sequence,
an = a1 + (n – 1)d ...... (1)
First term of the sequence is a1 = 12
Compute common difference as follows:
d = a2 – a1
= 20 – 12
= 8
Substitute a1 = 12, an = 172 and d = 8 in the formula (1) an = a1 – (n – 1)d and simplify,
172 = 12 + (n – 1)8
8(n – 1) = 160
n – 1 = 20
n = 21
Therefore, there are 21 terms in the given arithmetic sequence.