deletions | additions       diff --git a/Now_let_s_derive_x__.tex b/Now_let_s_derive_x__.tex  index 5a94cf2..4651e82 100644  --- a/Now_let_s_derive_x__.tex  +++ b/Now_let_s_derive_x__.tex 
...
$$\vec{x}(t + \Delta t) = 2 \vec{x}(t) - \vec{x}(t - \Delta t) + \vec{a}(t) \Delta t^2$$  which is \textit{exactly} (3). $\not{\Delta}$ $\not\Delta$