Coplanar

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 $\stackrel{\leftrightarrow }{PQ}$ and $\stackrel{\leftrightarrow }{RS}$ lie in the same plane $A$ .

They are coplanar .

Example 4:

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

They are non coplanar .