Answer
$\sum_{k=1}^{12} (2k-1)$
Work Step by Step
We need to compute summation formula for the sequence
$1+3+5+7+.......+[2(12)-1]$
When $k=1$, the first term is $1=(2)(1)-1$ and for $k=2$ , the second term is $3=(2)(2)-1$.
This information indicates the $k^{th}$ term as $(2k-1) $. So, we write the the summation formula for $k^{th}$ term as follows:
$1+3+5+7+.......+[2(12)-1]= \sum_{k=1}^{12} (2k-1)$
