The formula a_n = a_1 + (n  1)d can be used to give a formula for the general term of the arithmetic sequence. For example, the sequence 3, 15, 27, 39, 51,\dots has a_1 = 3 and common difference d = 12, hence a formula for the general term is given by a_n = 3 + (n  1)\cdotp 12 which simplifies: a_n = 12n  9. Now your turn: Which of the following is the general term b_n of the sequence 20, 18, 16, 14, 12, \dots?

×
b_n = 20  2n

×
b_n = 18n

✓
b_n = 22  2n

×
b_n = 18  2n