Coplanar lines are a set of lines that are in the same plane. The study of coplanar lines is done under the subject coplanar geometry. When two intersecting lines that must lie in the same plane therefore these 2 lines will be called coplanar. The definition of Coplanar is a set of points, lines, line segments, rays or any geometrical shapes are in the same plane they are known to be Coplanar. Parallel lines in the 3D space are coplanar. Skew lines are not coplanar. A set of lines drawn on the sheet of paper are coplanar.
The Points in the same plane are Coplanar therefore
a) Correct, Points A, B, C and D are coplanar
b) Incorrect, since both are in different plane
c) Correct, since both are in different plane
Example 2: Referring to the same figure in the above example, explain on which plane is the line OP coplanar.
In the given problem we can see 2 sets of planes. One is ABCD plane and 2nd
is EFGH plane. We see the line OP,
point O lies on line CD and GH. Point P lies on line AB and EF, therefore the line OP lies in the plane ABCD and EFGH.