\magnification=\magstep2

$$
\vec{r}_{AP} \quad \ne \quad \vec{r}_{BP}
$$

$$
\vec{r}_{AP} \quad = \quad \vec{r}_{AB} + \vec{r}_{BP}
$$

$$
\vec{r}_{AP} - \vec{r}_{BP} \quad = \quad \vec{r}_{AB} 
$$


$$
\vec{v}_{AP} - \vec{v}_{AB} \quad = \quad \vec{v}_{BP} 
$$

$$
\vec{v}_{AP} - \vec{v}_{BP} \quad = \quad \vec{v}_{AB} 
$$


\bye

