Alternate interior angles explained

Learn about the alternate interior angles. When comes to meaning of these three words I think you know what is alternate. Which means that one angle will be left and one more will be right of transversal. Interior means that inside and finally angle is union of two rays.

Alternate interior angles

How to define alternate interior angles? “The angles which are lying inside the two lines and lying opposite sides of transversal are called alternate interior angles”. By definition it may be some confusion so I explained by taking example. See the example you can understand still better.

Explanation of alternate interior angles with an example:

Consider any two lines namely L1 and L2 and also consider a transversal T1.

Alternate interior angles

From the diagram,

 (∠1, ∠2  )

(∠3, ∠4)

The above mentioned two pairs of angles are called alternate interior angles.


For checking the given lines are parallel or not, we can make use of these angles. If the alternate interior angles measures are equal then we can confirm that the given lines are parallel.

If you consider our example the lines L1 and L2 will be parallel when ∠1= ∠2  and  ∠3 = ∠4.

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