\documentclass[a4paper]{article}
\usepackage{tikz}
\begin{document}
\def\List{1, 2, 3}
List: \List  \par
Dim of List: \pgfmathparse{dim(\List)}\pgfmathresult

\bigskip
\def\List{200, 1, 3}
List: \List  \par
Dim of List: \pgfmathparse{dim(\List)}\pgfmathresult

\bigskip
Dim of 200: \pgfmathparse{dim(200)}\pgfmathresult
\end{document}

\documentclass{article}
\addtolength\textwidth{2cm}

\usepackage{multicol}
\usepackage{amsmath}


\begin{document}

\vspace*{-3cm}

A
\begin{multicols}{2}

\textbf{Linearity: }
\begin{align*}
y_1(t) &= u^2_1(t) \\
y_2(t) &= u^2_2(t) \\
u_3(t) &= c_1u_1(t) + c_2u_2(t) \\
y_3(t) &= u_3^2(t) \\
&= \left[c_1u_1(t) + c_2u_2(t)\right]^2 \\
&= c_1^2u_1^2(t) +2c_1c_2u_1(t)u_2(t)+ c_2^2u_2^2(t) \\
&\neq c_1y_1(t) + c_2y_2(t)
\end{align*}
The system is not linear.


\textbf{Time-Invariance}
\end{multicols}