Question

Write the explicit formula for the arithmetic sequence.

Arithmetic Sequence Formula a(n)= a(1) + d(n − 1)
-7, 2, 11, 20, ...

Answer 1

an = 9n -16

Explanation:

First find the common difference, d

Take the second term and subtract the first

2 - (-7) = 2+7 = 9

We are adding 9 each time

Check 2+9 =11, check 11+9 = 20 check

The first term in the sequence is a1 so a1 =-7

an = a1 + d(n-1)

an = -7 + 9(n-1)

Distribute

an = -7 +9n-9

Combine like terms

an = 9n -16