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Exterior Angles

Part of the Polygons & Quadrilaterals section of Coddy's Geometry journey. Lesson 11 of 61.

Extend one side of a polygon past a corner. The angle between the extension and the next side is an exterior angle. It measures how sharply you turn at that corner if you walk round the edge.

$Pentagon with side BC extended past C: interior angle 125 degrees, exterior angle 55 degrees$

The exterior angle and the polygon's own angle at that corner sit side by side on a straight line, so they add up to 180°. Here the angle at C is 125°, so the exterior angle is 180 - 125 = 55 degrees. Pick Angles on a straight line for it.

Challenge

Side AB of quadrilateral ABCD is extended past B. Find the exterior angle at B, marked ?, then press Check.

Try it yourself

$Find the marked part of the figure$

Find the marked part of the figure

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Polygons & Quadrilaterals

2Regular Polygons

Regular Polygons From an Angle to the Sides Inside a Regular Polygon Recap: Regular Polygons

5Rectangles, Rhombi, Squares

Rectangles The Diagonal of a Rectangle Rhombus Angles Squares Recap: Special Parallelograms

8Area of Parallelograms

Area of a Rectangle A Side from the Area Slide the Top Area of a Parallelogram Recap: Parallelogram Area

11Polygon Chases

Parallel Sides in a Pentagon Marks, Not Looks Pentagon with x Regular Shapes Together Recap: Polygon Chases

3Exterior Angles

Exterior AnglesExterior Angles Make 360°Regular Exterior Angles Sides from the Exterior Recap: Exterior Angles

6Trapezoids and Kites

Trapezoids Isosceles Trapezoids Trapezoids with x Kites Recap: Trapezoids and Kites

9Area of Trapezoids

Area of a Trapezoid A Missing Base Find the Height First Trapezoids by Area Recap: Trapezoid Area

12Final Challenges

Final: The Garden Bed Final: Enough to Finish?Final: The Ramp Final: The Gable Wall Final: The Star Point