Question

Write the sum using summation notation assuming the suggested pattern continues
9-18+36-72

Answer 1

i think it is 45 sorry if its wrong

Answer 2

Let's first work out the pattern. Since it's an geometric progression, we can find the sum to n terms of the pattern.


`S_n = (a(r^n - 1))/(r - 1)`

`S_n = (9((-2)^n - 1))/(-3)`

`S_n = -3((-2)^n - 1)`

Now that we've developed our geometric progression, we can start to add sigma notation.

k
∑(-3[(-2)^n - 1])
n = 1