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.