Question

Find the ninth partial sum of infinite sumnation 3i-4

Answer 1

$\bf \sum\limits_{i=1}^9\ 3i-4\implies \sum\limits_{i=1}^9\ 3i-\sum\limits_{i=1}^9\ 4\implies 3\sum\limits_{i=1}^9\ i-\sum\limits_{i=1}^9\ 4 \\\\\\ 3\cdot \cfrac{9(9+1)}{2}-(9\cdot 4)$

and surely you know how much that is.