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Transversal
A transversal line, in geometry, passes through two lines in the same plane at two distinct points. Transversals play a role in establishing the parallelism of two or more other straight lines in the Euclidean plane. It intersects two lines at distinct points. Intersection caused by transversal forms several angles. These are corresponding angles, alternate interior angles, alternate exterior angles, and cointerior angles.
1.  Transversals and Transversal Lines 
2.  Constructing a Transversal with Parallel Lines 
3.  Transversal Angles 
4.  FAQs on Transversal 
Transversals and Transversal Lines
In geometry, a transversal is any line that intersects two straight lines at distinct points. In the following figure, L is the transversal line that cuts \(L_{1}\) and \(L_{2}\) lines at two distinct points. In the universe of parallel and transverse lines, a transversal line connects the two parallel lines.
From the diagram, we can say that 'L is a transversal, cutting the lines \(L_{1}\) and \(L_{2}\)', and thus line L is the transversal line. Here, there is no relationship between the angles formed as the lines are not parallel. Let us now see how to construct a transversal on parallel lines and what are the properties of transversal angles.
Constructing a Transversal on Parallel Lines
The construction of a transversal is easy. First, we create two parallel lines. We construct the angle (at which we want to create the transversal) on the first line (say x) as shown.
Further, we extend this constructed angle up to a point it covers both the parallel lines as done here. Here is what we get: A transversal on the two parallel lines at the desired angle (x).
Transversal Angles
When a transversal cuts two parallel lines, several angles are formed by these two intersections. Those are called transversal angles. Those types of angles on a transversal are given below:
 Corresponding angles
 Alternate Interior Angles
 Alternate Exterior Angles
 Cointerior Angles
From the given diagram, if we try to organize the angles based on the relative positions they occupy, we get the following categories of angles :
Corresponding Angles
The following pairs of angles are corresponding angles:
 ∠1 and ∠5
 ∠2 and ∠6
 ∠3 and ∠7
 ∠4 and ∠8
Alternate Interior Angles
The following pairs of angles are alternate interior angles:
 ∠3 and ∠6
 ∠4 and ∠5
Alternate Exterior Angles
The following pairs of angles are alternate exterior angles:
 ∠1 and ∠8
 ∠2 and ∠7
Cointerior Angles
The following pairs of angles are cointerior angles:
 ∠3 and ∠5
 ∠4 and ∠6
Important Notes:
 A transversal is any line that intersects two straight lines at distinct points.
 A transversal that cuts the lines L_{1} and L_{2} is the transversal line.
 Intersection caused by transversals forms several angles. These are :
a) Corresponding Angles
b) Alternate Interior Angles
c) Alternate Exterior Angles
d) Cointerior Angles
Related Articles on Transversal
Check these interesting articles on transversal. Click to know more!
Transversal Examples

Example 1: Consider the following figure, in which M and N are parallel lines. What is the value of ∠C?
Solution: Through C, draw a line segment parallel to M and N, as shown below:
Now, AC and BC act as transversal interesting two parallel lines.
We have ∠y = ∠β = 60º (alternate interior angles) and ∠x = 180º – 120º (cointerior angles) ⇒ ∠x = 60º. Thus, we get ∠C = ∠x + ∠y = 120º. ∴ ∠C = 120º. 
Example 2: Consider the following figure, in which L, M, and N are parallel lines. The line AC is perpendicular to N, as shown. What are the values of ∠x, ∠y, and ∠z?
Solution: Since AC ⊥ N, it will be perpendicular to each of the other two parallels as well. AC is the transversal line to all the three parallel lines L, M, and N. This means that ∠x = 90º – 60º = 30º (as ∠LAC and ∠ACN are corresponding angles which are equal)
AN is also a transversal intersecting the three given parallel lines.
Now, ∠y = 180º – ∠x (cointerior angles)
⇒ ∠y = 150ºAlso, ∠z = ∠y = 150º (corresponding angles)
∴ The values of x, y, and z are 30°, 150°, and 150° respectively. 
Example 3: Consider the following figure, in which M  N. The angle bisectors of ∠BAX and ∠ABY intersect at C, as shown. Find the value of ∠ACB.
Solution: In the given figure, L is the transversal on two parallel lines M and N. We note that ∠BAX and ∠ABY are cointerior angles, which means that their sum is 180°.
⇒ ∠BAX + ∠ABY = 180º
⇒ 2(∠1 + ∠2) = 180º
⇒ ∠1 + ∠2 = 90ºNow, in ΔACB, we apply the angle sum property: ∠1 + ∠2 + ∠ACB = 180º
⇒ 90º + ∠ACB = 180º
⇒ ∠ACB = 90º
Therefore, the value of ∠ACB is 90 degrees.
FAQs on Transversal
Can Transversal Lines be Straight?
Yes, transversals are straight lines that intersect two or more lines at different points. A transversal line meets the other line at one point which forms four angles around the point of intersection.
How Many Angles are Formed by the Transversal?
The transversal forms several types of angles. Some of those angles are:
 Corresponding Angles
 Alternate Interior Angles
 Alternate Exterior Angles
 Cointerior Angles
What does Transversal Mean in Geometry?
In geometry, a transversal is a line, ray, or line segment that intersects other lines, rays, or line segments on a plane at different intersecting points. When it intersects parallel lines, there formed several angles that share a common property, on the other hand when a transversal intersects two or more nonparallel lines, there is no relationship between the angles formed.
How Many Angles are Formed by the Transversal?
When two parallel lines are intersected by the transversal, eight angles are formed. The eight angles include corresponding angles, alternate interior and exterior angles, vertically opposite angles, and cointerior angles.
Are Vertical Angles Formed by a Transversal Equal?
Vertical angles are always equal to each other in measure. When a transversal intersects a line, two pairs of vertical angles are formed.
Do Transversal Lines have to be Parallel?
No. Transversal lines can be at any angle to the given parallel lines. Thus, any 2 transversals need not be parallel.
What are Corresponding Angles in a Transversal?
Two or more angles that are on the same side of the transversal when it cuts two or more parallel lines are called corresponding angles. When a transversal intersects two parallel lines, four pairs of corresponding angles are formed.
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