\vec{v}

\vec{a}

A = (2, 1)
B = (6, 3)
a = Vector(A, B)
t = 0.5 (slider from -5 to 5)
v = Vector(A, A + (t * (B - A)))
a_1: x(a)
a_2: y(a)
Text1: "\textcolor{red}{\vec{v}}=\textcolor{#008000}{t}\cdot \textcolor{blue}{\vec a}=\textcolor{#008000}{" + (LaTeX[t]) + "}\cdot\textcolor{blue}{" + (LaTeX[a]) + "}=\textcolor{blue}{\pmatrix{\textcolor{#008000}{" + (LaTeX[t]) + "}\cdot" + (LaTeX[a_1]) + "\\\textcolor{#008000}{" + (LaTeX[t]) + "}\cdot" + (LaTeX[a_2]) + "}}=\textcolor{red}{" + (LaTeX[v]) + "}"