. What are Alternate Interior Angles?

Best Answer

When a transversal crosses parallel lines, the pair of angles form on the inner side of the parallel lines. However, on the opposite sides of the transversal are alternate interior angles. These angles are always equal. This can also be understood in another way. The alternate interior angles can prove the given lines are parallel or not. If these angles are equal, then the given lines crossed by a transversal are said to be parallel.

Observe the following figure to look at the alternate interior angles. Here AB and CD are parallel lines crossed by a transversal.

Alternate Interior Angles


By the alternate interior angle theorem, the pairs of alternate interior angles in the given figure are:

∠4 and ∠6

∠3 and ∠5



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