Question

Write the sum using summation notation, assuming the suggested pattern continues.

2, -10, 50, -250, +…

Is this sequence arithmetic or geometric? How do you know?

Answer 1

Explanation:

It's geometric. The nth term differs by -5 when compared to the n+1 term.

Sum 0 to n a(-5)^n-1 where a = 2

I think this is what you want, but there is also a formula. See below.

Sum = a (r^n - 1)/(r - 1)