Mastering Circles: From Circumference to Sectors
Mastering Circles: Shapes and Measures
Lesson duration is: 40 minItems in this lesson
Mastering Circles: Shapes and Measures
What do you already know about circles in geometry?
Learning Objective
At the end of the lesson you will be able to calculate the circumference and area of circles, and understand arcs, sectors, and segments.
Key Circle Vocabulary
A circle has important parts: centre, radius, and diameter. The radius is from the centre to the edge. The diameter is a line through the centre connecting two points on the circle.
Finding Circumference
Circumference is the distance around a circle. Use: C = 2 x r or C = x d.
Calculating Area of a Circle
The area is the space inside the circle. Formula: A = x r b2.
Arcs and Sectors
An arc is a part of the edge. A sector is a 'slice' defined by two radii and an arc. Their lengths and areas depend on the angle.
Calculating Arcs and Sectors
Finding Arc Length
Sector area 3d (Angle b0/360 b0) x Area of circle.
Arc length 3d (Angle b0/360 b0) x Circumference.
Finding Sector Area
What is a Segment?
A segment is the region between a chord (straight line across the circle) and the arc above it.
Summary and Reflection
You can now describe and calculate parts of circles: circumference, area, arcs, sectors, and segments. Where do you see circles used in real life?
Write down 3 things you learned in this lesson.
Write down 2 things you want to know more about.
Ask 1 question about something you haven't quite understood yet.
