Question

What is the sum of the first n positive integers? [1 MARK]

Answer 1

Formula: 0.5 Mark
Application: 0.5 Mark

$S=1+2+3+....+n$

$S=\frac{n}{2}\left(\text{first term + last term}\right)$

$S=\frac{n}{2}(1+n)$

$S=\frac{n(n+1)}{2}$