Question

Find the series shown.

7 + 9 + 11 + 13 + 15
11 + 13 + 15 + 17 + 19
11 + 13 + 15 + 17 + ...
7 + 9 + 11 + 13 + ...

Answer 1

C
`11+13+15+17+...`

Explanation:

Consider the series

`\sum\limits_(n=3)^(\infty)(2n+5)`

The nth term of series is
`a_n=2n+5`

The bottom index tells you that n starts changing from 3, so

`a_3=2\cdor 3+5=11\\ \\a_4=2\cdot 4+5=13\\ \\a_5=2\cdot 5+5=15\\ \\a_6=2\cdot 6+5=17\\ \\...`

Thus, the sum of all terms is

`11+13+15+17+...`