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Neighbouring Angles

Part of the Polygons & Quadrilaterals section of Coddy's Geometry journey. Lesson 17 of 61.

In parallelogram ABCD, the side AB crosses the parallel sides AD and BC. The angles at A and at B both lie between those parallels and on the same side of AB, so they are co-interior angles, and co-interior angles add up to 180°.

$Parallelogram ABCD with angles of 70 degrees at A and 110 degrees at B$

Here ∠A is 70°, so ∠B is 180 - 70 = 110 degrees. The same holds along every side: any two neighbouring angles of a parallelogram add up to 180°. Pick Co-interior angles for it.

Challenge

ABCD is a parallelogram. Find the 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