Math Help - Help with reversing an equation

1. Help with reversing an equation

Hello,

I need some help with the following equation:

n * (( n / 2 ) + 0.5) = TN

Thus:

15 * (( 7.5 ) + 0.5 ) = 120

I would like to be able to have TN and solve for n. I couldn't figure out a way to reverse the equation or isolate n.

Can anyone help me with this please?

2. $\begin{gathered}
n\left( {.5n + .5} \right) = T \hfill \\
n^2 + n - 2T = 0 \hfill \\
n = \frac{{ - 1 + \sqrt {1 + 8T} }}
{2} \hfill \\
\end{gathered}$

3. Thanks