I1.1 If the sum of the interior angles of an $n$-sided polygon is $1440^{\circ}$, find $n$.
I1.2 If $x^{2}-n x+a=0$ has 2 equal roots, find $a$.
$\begin{array}{l}180^{\circ} \times(n-2)=1440^{\circ} \\ \Rightarrow n=10 \\ (-10)^{2}-4 a=0 \\ \Rightarrow a=25\end{array}$