# Coplanar

Points or lines are said to be coplanar if they lie in the same plane.

Example 1:

The points $P$, $Q$, and $R$ lie in the same plane $A$.

They are coplanar.

Example 2:

The points $P$, $Q$ and $R$ lie in the plane $A$ and the point $S$ lies on the plane $B$.

They are non coplanar.

Example 3:

The two lines $\stackrel{↔}{PQ}$ and $\stackrel{↔}{RS}$ lie in the same plane $A$.

They are coplanar.

Example 4:

The two lines $\stackrel{↔}{PQ}$ and $\stackrel{↔}{UV}$ are skew lines.

They are non coplanar.