Trapezoids with x

Part of the Polygons & Quadrilaterals section of Coddy's Geometry journey. Lesson 29 of 61.

Letters in a trapezoid's angles work like any angle labels. Find the rule that links the labelled angles, and it writes the equation.

$Trapezoid with angles 3x and x plus 40 degrees along the leg BC$

Here the angles at B and C lie along the leg BC, between the parallel bases, so they are co-interior: 3x + (x + 40) = 180. Collect: 4x + 40 = 180, so 4x = 140 and x = 35. The angles are 105° and 75°.

Challenge

ABCD is a trapezoid with AB ∥ DC. Tap the two labelled angles, pick the rule that connects them, and solve the equation the board writes for x.

Then press Check.

Try it yourself

$Use the figure to find x$

Use the figure to find x

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

6Trapezoids and Kites

Trapezoids Isosceles TrapezoidsTrapezoids with xKites 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