​ What is ∑n=18(3n−1) equal to?

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 a_n 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