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Parallelograms with x

Part of the Polygons & Quadrilaterals section of Coddy's Geometry journey. Lesson 17 of 59.

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 $2x+\left(x+30\right) = 180$ . 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

All lessons in Polygons & Quadrilaterals

1Polygons

Angles of a Quadrilateral Angles in Any Polygon How Many Sides?Polygon Angles with x Recap: Polygon Angles

4Parallelograms

Parallelograms Neighbouring Angles Opposite AnglesParallelograms with xA Diagonal Inside Recap: Parallelograms

7On Squared Paper

Make a Parallelogram Draw a Tilted Rectangle Draw a Rhombus Draw a Trapezoid and Kite Recap: Squared Paper

10Composite Shapes

Shapes Made of Parts Rectangle and Triangle Area by Subtracting Enough to Find It?Recap: Composite Shapes

2Regular Polygons

Regular Polygons 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