# Circle Theorems: Angle in a semicircle is 90 degrees

In this lesson, we will learn that the angle in a semicircle is 90 degrees when the angle is subtended from the diameter. We will prove this result with a general case.

Quiz:

# Intro quiz - Recap from previous lesson

Before we start this lesson, let’s see what you can remember from this topic. Here’s a quick quiz!

Q1.Work out the size of angle x.

1/3

Q2.Work out the size of angle x.

2/3

Q3.Work out the size of angle x.

3/3

Quiz:

# Intro quiz - Recap from previous lesson

Before we start this lesson, let’s see what you can remember from this topic. Here’s a quick quiz!

Q1.Work out the size of angle x.

1/3

Q2.Work out the size of angle x.

2/3

Q3.Work out the size of angle x.

3/3

# Video

Click on the play button to start the video. If your teacher asks you to pause the video and look at the worksheet you should:

• Click "Close Video"
• Click "Next" to view the activity

Your video will re-appear on the next page, and will stay paused in the right place.

# Worksheet

These slides will take you through some tasks for the lesson. If you need to re-play the video, click the ‘Resume Video’ icon. If you are asked to add answers to the slides, first download or print out the worksheet. Once you have finished all the tasks, click ‘Next’ below.

Quiz:

# Circle Theorems: Angle in a semicircle is 90º

Don’t worry if you get a question wrong! Forgetting is an important step in learning. We will recap next lesson.

Q1.Work out the size of angle x.

1/3

Q2.Work out the size of angle y.

2/3

Q3.Work out the size of angle x.

3/3

Quiz:

# Circle Theorems: Angle in a semicircle is 90º

Don’t worry if you get a question wrong! Forgetting is an important step in learning. We will recap next lesson.

Q1.Work out the size of angle x.

1/3

Q2.Work out the size of angle y.

2/3

Q3.Work out the size of angle x.

3/3

# Lesson summary: Circle Theorems: Angle in a semicircle is 90 degrees

## Time to move!

Did you know that exercise helps your concentration and ability to learn?

For 5 mins...

Move around:
Jog

On the spot:
Chair yoga