c$++$

The Triangle Sum Challenge.

$T_n,$ the $n^{th}$ triangle number, is the number of points required to construct a

triangle with $n$ dots on each side $($see Figure $1).$ In particular, the sum of integers

from $1$ to $n$ is as follows.

$T_n={\displaystyle \underset{i=1}{\overset{n}{}}}i$

Write a recursive function int triangleNum$($int $n)$ that returns $T_n.$

$-08$

$T_1-1,T_2-3,T_4-6,T_4-10$

Figure $1$: The Triangle Challenge