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Find the 18th term.
-21, -14, -7, 0, 7, ...
18th term = [?]

User Bdkosher
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1 Answer

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The 18th term is 98.

An arithmetic sequence is a sequence of numbers in which the difference of any two successive members is a constant. This sequence starts with -21, and each subsequent number increases by 7.

The formula for the nth term of an arithmetic sequence is:

a_n = a_1 + (n - 1) * d

where:
- a_n is the nth term we're trying to find
- a_1 is the first term in the sequence
- d is the common difference
- n is the position of the term in the sequence

Let's plug in the given values into the formula:

First term, a_1 = -21
Common difference, d = 7
We're looking for the 18th term, so n = 18

Now, we can calculate:

a_18 = -21 + (18 - 1) * 7

Doing the operations in parentheses first:

a_18 = -21 + 17 * 7

Then multiplication:

a_18 = -21 + 119

And lastly, addition:

a_18 = 98

So, the 18th term of the given arithmetic sequence is 98.

User Sjoerd Pottuit
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