Before you study this topic, you are advised to read:
Interior Angles of a Triangle
Exterior Angles of a Triangle
In the following diagram you can see exterior angles and interior angles.
Adjacent Interior Angles are shown with diagram in following:
In the below diagram you can see that ∠ 2 is an exterior angle.
So, ∠ 3 is Adjacent Interior Angle to ∠ 2
In the below diagram you can see that ∠ 6 is an exterior angle.
So, ∠ 5 is Adjacent Interior Angle to ∠ 6
In the below diagram you can see that ∠ 1 is an exterior angle.
So, ∠ 1 is Adjacent Interior Angle to ∠ 4
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