Proof of Alternate Exterior Angle Equal

Last updated at August 14, 2026 by

Let’s prove alternate exterior angles ∠1 & ∠8 equal

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For parallel lines l and m,

with transversal p,

  ∠1 = ∠5       (Corresponding angles)  …(1)

 

Also,

  ∠5 = ∠8               (Vertically opposite angles)  …(2)

 

From (1) & (2)

  ∠1 = ∠5

Proof of Alternate Exterior Angle Equal - Part 2

 

Hence,

Alternate Exterior Angles are equal. 

 

 

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