Parallelograms with x

Part of the Polygons & Quadrilaterals section of Coddy's Geometry journey. Lesson 19 of 61.

When the angles of a parallelogram carry a letter, the co-interior rule writes the equation. Neighbouring angles add up to 180, so their labels do too.

$Parallelogram with angles 2x and x plus 30 degrees at A and B$

Here 2x + (x + 30) = 180. Collect the terms: 3x + 30 = 180, so 3x = 150 and x = 50. The angles are 100° and 80°, and they add up to 180°.

Challenge

ABCD is a parallelogram. 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