# How do you find the 8th term of -1, 1, 3, ...?

Mar 2, 2018

The 8th term in the sequence, ${a}_{8}$, is 13.

#### Explanation:

This appears to be an arithmetic sequence, as the numbers are increasing by 2 each time.

The formula for finding the $n$th term in an arithmetic sequence is:

${a}_{n} = {a}_{1} + \left(n - 1\right) d$

${a}_{1}$, the first term in this sequence is -1.

$d$, or the common difference is 2.

Plug this information into the formula:

${a}_{n} = - 1 + \left(n - 1\right) 2$

${a}_{n} = 2 n - 3$

Now plug in 8 for $n$ to find ${a}_{8}$, or the 8th term in the sequence:

${a}_{8} = 2 \left(8\right) - 3$

${a}_{8} = 13$