Below is a picture of the triangle in R3 whose vertices are the points p and q and r. This picture is
very easy to create using a command in the plots package. Find this command yourself: look at the list of commands in plots, guess, and then use help. A hint: The command you're looking for can do more than triangles. It can also plot quadrilaterals, pentagons, hexagons, and many other two-dimensional shapes in three dimensions.