1. use the above figure to answer the following questions.

a. what is the intersection of plane p and plane r?

b. name three points that are collinear

c. name plane r in two more ways

d. name four coplanar points

e. name a point that lies on both plane p and plane r

A. Plane R and plane P intersect at AB. 
Planes are when 3 points that are not on the same line can be used to describe a plane. Plane P is horizontal and Plane R is vertical and these 2 planes intersect at line AB. Intersecting is where these 2 planes meet, therefore line AB is common to both planes.

b. 3 points that are collinear are A, D and B. As the word collinear implies, this is when three points or more are all aligned in a single straight line. 

c. Planes can be named indicating three points that are on the same plane yet not on the same line. In other words these points are not collinear. Plane R can be written as DBG or FAD.

d.Coplanar points are three or more points that lie on the same plane. planes are usually flat surfaces, therefore any three or more points lying on this flat surface be used as coplanar points. 4 coplanar points are ACDE, these lie on plane P.

e. A point that lies on both plane P and plane R is point D, as its on the line of intersection, hence its common to both planes.