Question 1063647
The line over {{{P[1]P[2]}}} means
that they are talking about the line segment
joining those two points.


You are looking for the coordinates of a point {{{R}}} ,
on that line segment that meets the requirement that
{{{P[2]R/RP[2]=3/1}}} .
In other words, 
the distance from {{{R}}} to {{{P[1]}}} is {{{3}}} times
the distance from {{{R}}} to {{{P[2]}}} .
Dividing the original segment into
{{{3+1=4}}} equal pieces, {{{R}}} is
the"dividing point" closest to {{{P[2]}}} .
In this case, if {{{M}}} is the midpoint of segment P1P2,
{{{R}}} is the midpoint of segment MP2.