Transversal t cuts two parallel lines, a and b.

In geometry, a transversal line is a line going through two or more other coplanar lines at different points. Normally, the two lines are not only coplanar, but also parallel. Two parallel lines cut by a transversal, with plenty of labels. ... Two parallel lines cut by a transversal, with plenty of labels. ... Geometry (from the Greek words Geo = earth and metro = measure) is the branch of mathematics first popularized in ancient Greek culture by Thales (circa 624-547 BC) dealing with spatial relationships. ... A set of points is said to be coplanar if and only if they lie on the same geometric plane. ... Parallel is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. ...

We know that a is parallel to b, so if a transversal t crosses a with angle θ, then it must also cross b with angle θ. This leads to the relationships shown in the picture; interior angles add up to 180 degrees, exterior angles add up to 180 degrees, and corresponding angles (angles in the same position) are congruent. In geometry, an internal angle is an angle that 2 sides of a polygon form by touching. ... See also: congruence relation In geometry, two shapes are called congruent if one can be transformed into the other by a series of translations, rotations and reflections. ...