Question

Write the sum using summation notation, assuming the suggested pattern continues. -9 - 3 + 3 + 9 + ... + 81

Answer 1

Answer:

Option A:        $\sum_{n = 1}^{15} {\textbf{- 9 + 6 n}}$

Step-by-step explanation:

We are given with the series - 9  - 3  + 3   +  9 +  . . . .  +  81.

Note that the second term is obtained by adding 6 to the first term.

Each consecutive term is obtained by adding 6 to its previous term.

Therefore, we should be adding six two times to get the third term from the first term.

Putting it Mathematically, we get: - 9 + 6n

This gives all the terms of the sequence. Since, we have to add all the terms we take the summation.

Also, note that 81 is the 15 th term.

Therefore, - 9  - 3  + 3   +  9 +  . . . .  +  81 =    $\sum_{n = 1}^{15} {- 9 + 6 n}$

Hence, the answer.