Question

Write an
explicit formula for an, the nth term of the sequence 21, 27, 33, ....

Answer 1

Explanation:

Remark

This is an arithmetic series. Each term differs by 6 from the previous one.

Givens

a1 = 21

d = 6

Formula

a_n = a1 + (n - 1)*d

Sample

Try it.

Let's let n = 3 which we have the answer for.

a_3 = 21 + (3-1)*6

a_3 = 21 + 2 * 6

a_3 = 21 + 12

a_3 = 33

That's exactly what the 3rd term is.