Question

What is the sum of all the elements of the 9th term, which has 9 elements in it, of the following sequence:
(1), (3,5), (7,9,11), (13,15,17,19), ⋯?

Answer 1

well, the terms seem to be 2 apart in each element

Answer 2

1 3 7 13
2 4 6 im going with add 8 next

Answer 3

Note that we are basically summing up all the terms from n = 37 to n = 45 in the arithmetic sequence: \(\bf a_n=1+(n-1)2\). But we can define our arithmetic sequence such that it starts at the 37th term. We know that \(\bf a_{37}=73\) so we can define a new arithmetic sequence as \(\bf a_n=73+(n-1)2\) and sum up the first 9 terms of this sequence using the arithmetic sum formula \(\bf S_n=\frac{n}{2}(2a+n-1(d))=\frac{n}{2}(146+(n-1)2)\). Evaluate the sum for n = 9 and that will be your answer.

Answer 4

@denis1206

Answer 5

corect