Question

What is the sum of the arithmetic series? ∑[i=1,15,Fn=5i-1]

Answer 1

$\bf \sum\limits_{i=1}^{15}\ 5i-1\implies 5\sum\limits_{i=1}^{15}\ i-\sum\limits_{i=1}^{15}\ 1\implies 5\left[ \cfrac{15(15+1)}{2} \right]-(15\cdot 1) \\\\\\ 5\cdot (15\cdot 8)-15\implies 585$