SOLUTION: Write the following sum with summation notation: 2 - 12 + 72 - 432 + 2592 - 15552. The index here is 1. I do notice the pattern of multiplying -6 to get the following integers

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Question 1086516: Write the following sum with summation notation: 2 - 12 + 72 - 432 + 2592 - 15552.
The index here is 1. I do notice the pattern of multiplying -6 to get the following integers after 2, but I am having trouble finding f(i).

Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
Use (-1)^a power to generate opposite signs for successive terms.
(-1)^(n-1)*2*6^(n-1)
n=1; 2
n=2:-2*6^1
n=3:+2*6^2

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