TeX source:

{q_s}(t) =\left\{ \begin{array}{lll} (p_s−p_m)t, & 0 ≤ t ≤ t_s \\ p_m (T_s - t), & t_{s} ≤ t ≤ T_s \\ 0, & T_s ≤ t ≤ T \end{array} \right.