Question

The simple formula for the nth term of an arithmetic sequence is an = 5n + 15. What is the explicit formula corresponding to the simple formula?

A. an = 15 + 5n
B. an = 15 + (n - 1)(5)
C. an = 20 + (n)/(5)
D. an = 20 + (n - 1)(5)
E. an = 5 + (n - 1)(15)

Answer 1

Sequence will look like this:
Term 1: 20 --------- 20 + 5(0)
Term 2: 25 --------- 20 + 5(1)
Term 3: 30 --------- 20 + 5(2)
Term 4: 35 --------- 25 + 5(3)
ETC.

It cab noted that the numbers in the bracket (that is, 0, 1, 2, 3, 3, etc) = n-1

Then, the explicit formula will be;
an = 20 + 5(n-1).

The correct answer is D.