How to identify parallel lines, a line parallel to a plane, and two parallel planes.
How to take the converse of the parallel lines theorem.
How to mark parallel lines, how to show lines are parallel, and how to compare skew and parallel lines.
How to determine whether two lines in space are parallel or perpendicular.
How to find the angle between planes, and how to determine if two planes are parallel or perpendicular.
How to find the resultant of two forces when they are parallel, opposite, or perpendicular in direction.
How to write an equation for the coordinate planes or any plane that is parallel to one.