Same-Side Exterior Angles: Definition & Theorem

Same-Side Exterior Angles: Definition & Theorem
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  • 0:00 What Are Same-Side…
  • 1:04 Theorem
  • 1:36 Example
  • 2:10 Lesson Summary
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Lesson Transcript
Instructor: Mia Primas

Mia has taught math and science and has a Master's Degree in Secondary Teaching.

Many kinds of angles are formed by intersecting lines. In this lesson, you'll learn the definition and theorem of same-side exterior angles. Then, take a brief quiz to check what you learned.

What Are Same-Side Exterior Angles?

When two parallel lines are cut by a third intersecting line, called a transversal line, eight angles are formed. These angles form different relationships with each other, one of them being same-side exterior. Same-side tells us that both angles are on the same side of the transversal line, and exterior tells us that both angles are exterior, or outside, of the parallel lines.

Let's think of the parallel lines as hamburger buns. If the angles are outside of the buns, they are exterior. If they are inside the buns, they would be considered interior. In the following figure, angles a, b, c, and d are exterior to the parallel lines.

In this figure, angles a and c are on the same side of the transversal line, so they have a same-side exterior relationship. Angles b and d also have a same-side exterior relationship.

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