1,2=4,8t-1/2*9,81*t*t

 

$$\\1.2=4.8t-1/2*9.81*t*t\\
1.2=4.8t-4.905t^2\\
4.905t^2-4.8t+1.2=0\\$$

 

$${\mathtt{4.905}}{\mathtt{\,\times\,}}{{\mathtt{t}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{4.8}}{\mathtt{\,\times\,}}{\mathtt{t}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1.2}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = {\mathtt{\,-\,}}{\frac{\left({\mathtt{4}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{35}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,-\,}}{\mathtt{160}}\right)}{{\mathtt{327}}}}\\
{\mathtt{t}} = {\frac{\left({\mathtt{4}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{35}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{160}}\right)}{{\mathtt{327}}}}\\
\end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = {\mathtt{\,-\,}}\left({\mathtt{\,-\,}}{\frac{{\mathtt{160}}}{{\mathtt{327}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{0.072\: \!367\: \!948\: \!417\: \!379\: \!7}}{i}\right)\\
{\mathtt{t}} = {\frac{{\mathtt{160}}}{{\mathtt{327}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{0.072\: \!367\: \!948\: \!417\: \!379\: \!7}}{i}\\
\end{array} \right\}$$

There are 2 complex roots BUT NO REAL ROOTS