Question

PLEASE NEED HELP!!!

What is ∑ (3n−1) equal to?

n=18 is on bottom
8 is on top

Answer 1

`a_(1) = 3(1)-1=2`

`a_(8) =3(8)-1=24-1=23`

`S_(8) = (8)/(2)(23+2)=4(25)=100`

Your answer is 100

Answer 2

So basically this is sigma, or summation notation, and if you still don't know what it is:

Start at the number on the bottom. Plug in that number to the equation on the right, plug in the next number into the equation on the right, and so on, until you get to the number on top. Plug in that final number, and after you get the solution, add all the solutions you have all together.
One thing though: the bottom number cannot be bigger than the number on top.

Plug in 1: 3 x (1) - 1 = 2
Plug in 2: 3 x (2) - 1 = 5
Plug in 3: 3 x (3) - 1 = 8

and so on. the pattern goes by +3

2 + 5 + 8 + 11 + 14 + 17 + 20 + 23 = 100

Answer is 100.