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# ​ What is ∑n=18(3n−1) equal to?

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What is ∑n=18(3n−1) equal to?

Hev123  May 16, 2018
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Hey Hev!

We can see this is an arithmetic sequence,

It is obvious because the formula in the summation notation gives us the formula, 3n - 1

We just need to find the sum of the 8 terms.

To find the sum of an arithmetic sequence, we use the formula:

$$S_n=\frac{n}2(a_1+a_n)$$, where $$S_n$$ is the sum, n is the number of terms, a1 is the first term, and an is the last term.

We plug in the values of n into the formula, to find the term value.

$$S_n=\frac82(2+23)=100$$, that is your final answer.

I hope this helped,

Gavin

GYanggg  May 16, 2018