Generalize This!

Algebra Level 3

$(x-1)(x-2) \cdot \cdot \cdot (x-n)$

The coefficients of $x^{n-2}$ in the expansion above is equals to?

\dfrac{1}{2} \left \{\left (\sum{n} \right )^2- \sum{n^2} \right \}

\sum{n^2}

\left (\sum{n} \right)^2 - \sum{n^2}

\left (\sum{n} \right )^2