Review the basics of vertical angles, and try some practice problems.

Vertical angles

Vertical angles are angles opposite each other where two lines cross.
For example, AXD\angle AXD and BXC\angle BXC are vertical angles in the following diagram:
Want to learn more about vertical angles? Check out this video.

Practice set

Problem 1A
Are APD\angle APD and CPB\angle CPB vertical angles?
All segments that appear straight are straight.
Choose 1 answer:
Choose 1 answer:
Want to try more problems like this? Check out this exercise.

Use vertical angles to find a missing angle measure

Let's look at an example.
What is the measure of angle xx?
First, let's find the measure of the pink angle:
The pink and blue angles add up to 180180^\circ because they are adjacent and form a straight line.
pink angle=180121=59 \pink{\text{pink angle}} = 180^{\circ} - \blue{121^{\circ}} = \green{59^{\circ}}
The pink and green angles also add up to 180180^\circ because they are adjacent and form a straight line too.
green angle=18059=121 \green{\text{green angle}}= 180^{\circ} - \pink{59^{\circ}} = \green{121^{\circ}}
The measure of angle x=121x=\green{121^{\circ}}.

Practice

Problem 2A
What is the measure of angle xx?
\Large{^\circ}
Vertical angles are always equivalent!
Want to try more problems like this? Check out this exercise.