$${\mathtt{v}} = {\sqrt{{{\mathtt{vx}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{{\mathtt{g}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{{\mathtt{t}}}^{{\mathtt{2}}}}}$$ 1.) quadrieren
$${{\mathtt{v}}}^{{\mathtt{2}}} = {{\mathtt{vx}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{{\mathtt{g}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{{\mathtt{t}}}^{{\mathtt{2}}}$$ 2.) minus g^2*t^2
$${{\mathtt{vx}}}^{{\mathtt{2}}} = {{\mathtt{v}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{{\mathtt{g}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{{\mathtt{t}}}^{{\mathtt{2}}}$$ 3.) Wurzel ziehen (radizieren)
$${\mathtt{vx}} = {\sqrt{{{\mathtt{v}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{{\mathtt{g}}}^{{\mathtt{2}}}{\mathtt{\,\times\,}}{{\mathtt{t}}}^{{\mathtt{2}}}}}$$
Zufrieden? Gruß radix ! ( der sich auch über eine Antwort freut.)