Circles
Radius, circumference, area, sectors, annuli and the angles of a circle
The Circles unit belongs to the Geometry and trigonometry section of Math Mental and has 28 lessons: radius, circumference, area, sectors, annuli and the angles of a circle.
Lessons in this unit
- From the diameter to the radius
- From the radius to the diameter
- Parts of a circle
- Circumference in terms of π
- Circumference from the diameter
- Circumference with π = 3.14
- From the circumference to the radius
- Practice: radius and circumference
- Area in terms of π
- Area from the diameter
- Area with π = 3.14
- From the area to the radius
- Arc length
- Area of a sector
- Sector with π = 3.14
- From the sector to the central angle
- Area of an annulus
- Annulus with π = 3.14
- From the annulus to the outer radius
- Practice: sectors and annuli
- Central angle
- Inscribed angle
- Angle in a semicircle
- Turns of a wheel
- A slice of pizza
- Laps on the track
- Circle review
- Circle test
How to work through this unit
Follow the lesson order
The unit has 28 lessons of increasing difficulty. Finish one before moving on: the early techniques come back in the later questions.
Solve it before reading the solution
Work every question out on your own, then read the step by step and check the reason for each step instead of only comparing the final answer.
Lock it in during review
The question types you miss come back in practice and review until you get them right in a row. The unit test confirms the whole unit stuck.
Frequently asked questions about this unit
What does the Circles unit cover?
Circles belongs to the Geometry and trigonometry section and has 28 lessons: radius, circumference, area, sectors, annuli and the angles of a circle. The lessons start with the basic cases and build up to applications, always with a step-by-step solution.
What should I know before studying Circles?
This page names the previous unit on the path. If it is not solid yet, go back and practice first; if there is no prerequisite, this is where the path begins.
How long does Circles take?
Each lesson takes a few minutes. Most students do one or two a day and finish a unit in one or two weeks. The goal is answering correctly day after day, not clearing everything at once.
Are the Circles exercises free?
Yes. Every Math Mental lesson is free and ad-free; you only need an account to save your progress.
Your first lesson takes five minutes
Create an account, pick where to start and keep your streak from today.