Question

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

-4 + 5 + 14 + 23 + ... + 131

Answer 1

First element is -4
Second elemnt is -4 + 9
Third element is -4 + 9 + 9
Nth element is -4 + 9*(n-1)

Lets look at 131:
131 = -4 + 9*(n-1) --> n-1 = 15 --> n=16
So 131 is the 16th element

\[\sum_{1}^{16} -4+9(n-1) = \sum_{1}^{16} -4+9n-9 = \sum_{1}^{16} 9n-13\]

Answer 2

Okay, that is the same answer I obtained, however it is not one of my choices.

Answer 3

Send your choices, let me have look at them

Answer 4

Okay

Answer 5

Wow, I accidentally closed this.

Answer 6

\[\sum_{n=1}^{16} 9n-13 \rightarrow \sum_{k=0}^{15} 9k-4 \rightarrow \sum_{n=0}^{15} 9n-4\]

There is a secret n in the top of the summation symbol. So 16 becomes 15

Answer 7

Okay, Thank You so much !