Find the sum of the geometrical equation - 3, 18, - 108, if there are 7 terms

Hello from MrBillDoesMath!

Answer:

Sum = - 119,962 (I hope!)

Discussion:

Let's determine the pattern.

first term: - 3

2nd term: (-3) * (-6) = 18 (multiply first term by - 6)

3rd term: (18) * (-6) = - 108 (multiply 2nd term by - 6)

4th term : (-108) * (-6) = 648 (etc)

5th term : (648) * (-6) = - 3888 (etc)

6th term : (-3888) * (-6) = 23328 (etc)

7th term: (23328) * (-6) = - 139967 (etc)

Sum = - 119,962

A simpler way to do this is to use the formula for the sum of a geometric series to n terms. The series is

-3 Sum (-6) ^n n = 0, 1, 2, 3, 4, 5, 6

Regards,

MrB

P. S. I'll be on vacation from Friday, Dec 22 to Jan 2, 2019. Have a Great New Year!