deletions | additions       diff --git a/From_3_vec_a_t__.tex b/From_3_vec_a_t__.tex  index 0a84626..ff4079e 100644  --- a/From_3_vec_a_t__.tex  +++ b/From_3_vec_a_t__.tex 
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From (3):  $$\vec a(t)\Delta t^2=\vec{x}(t+\Delta t) - 2\vec x(t) + \vec x(t-\Delta t)$$  $$\vec a(t+\Delta t)\Delta t^2=\vec{x}(t+2 \Delta t) - 2\vec x(t+\Delta t) + \vec x(t)$$ $$(\vec a(t) + \vec a(t+\Delta t))\Delta t^2= \vec x(t-\Delta t) - \vec x(t) + \vec{x}(t+2 \Delta t) - \vec x(t+\Delta t) $$