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Ellah Marie Ardaniel
12/1/2025
Geometry
BASIC PARTS OF A CIRCLE
231
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Dec 1, 2025
•
Understanding the Key Parts of a Circle
Ellah Marie Ardaniel
@ellahmri
1 / 3
Basic Parts of a Circle
Think of a circle as a perfectly round shape where every point on the edge is exactly the same distance from the centre - it's like drawing around a coin but mathematically perfect! We name circles after their centre point, so if the centre is point A, we call it "circle A" and write it as ⊙A.
You can create circles using a compass - that handy maths tool that keeps one point fixed while the other draws the perfect curve. Every circle naturally divides space into three parts: the interior (inside the circle), the exterior (outside the circle), and the circle itself.
The radius is probably the most important measurement you'll work with. It's any straight line from the centre to the edge of the circle, and here's the brilliant bit - all radii in the same circle are exactly the same length! Whether you measure from the centre to any point on the circle, you'll always get the same distance.
A chord is simply any straight line that connects two points on the circle. Think of it like a guitar string stretched across the circular sound hole - it doesn't have to go through the centre, just connect any two points on the edge.
Quick Tip: Remember that radius is singular, but when talking about multiple radii, the plural form is "radii" - this often trips students up in exams!
Diameters, Arcs, and Angles
A diameter is basically the biggest chord possible - it's a straight line that goes right through the centre, touching both sides of the circle. Since it's made of two radii joined together, the diameter is always twice as long as the radius.
An arc is simply any curved section of the circle - imagine taking a slice of the circle's edge. There are three types you need to know: minor arcs (less than half the circle), semicircles (exactly half), and major arcs (more than half). It's like cutting a pizza - small slice, half pizza, or most of the pizza!
Central angles are formed when you draw two radii from the centre, creating an angle with its tip right at the centre. These are super important because they help us measure how big an arc is.
Inscribed angles are different - they're formed by two chords meeting at a point on the circle itself, not at the centre. Picture standing on the edge of a circular field and looking at two different points - the angle you're looking through is an inscribed angle.
Memory Trick: Central angles have their vertex at the "central" point (the centre), while inscribed angles are "written on" the circle itself!
Lines and Circles
When lines interact with circles, they can do so in two main ways, and understanding this difference is crucial for solving geometry problems.
A secant line is like an arrow that shoots straight through the circle, intersecting it at exactly two points. The bit of the secant line between these two intersection points is actually a chord - so every secant line contains a chord within the circle.
A tangent line is much more gentle - it just barely touches the circle at exactly one point, like a ball rolling along a wall. This single touching point is called the point of tangency, and it's special because the tangent line is always perpendicular to the radius at this point.
These concepts might seem simple, but they're the foundation for loads of advanced circle theorems you'll encounter later. Being able to quickly identify whether a line is a secant or tangent will save you tons of time in problem-solving.
Real-world Connection: Think of a bicycle wheel - the spokes are radii, the rim is the circle, and when the wheel touches the ground, that's a tangent line with the ground as the point of tangency!
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Stefan S
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
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Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
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Greenlight Bonnie
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Aubrey
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Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
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Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
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Marco B
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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Understanding the Key Parts of a Circle
Ellah Marie Ardaniel
@ellahmri
Ever wonder how mathematicians define those perfect round shapes you see everywhere? Circles are actually one of the most fascinating shapes in geometry, and understanding their parts will help you tackle loads of maths problems with confidence.
Basic Parts of a Circle
Think of a circle as a perfectly round shape where every point on the edge is exactly the same distance from the centre - it's like drawing around a coin but mathematically perfect! We name circles after their centre point, so if the centre is point A, we call it "circle A" and write it as ⊙A.
You can create circles using a compass - that handy maths tool that keeps one point fixed while the other draws the perfect curve. Every circle naturally divides space into three parts: the interior (inside the circle), the exterior (outside the circle), and the circle itself.
The radius is probably the most important measurement you'll work with. It's any straight line from the centre to the edge of the circle, and here's the brilliant bit - all radii in the same circle are exactly the same length! Whether you measure from the centre to any point on the circle, you'll always get the same distance.
A chord is simply any straight line that connects two points on the circle. Think of it like a guitar string stretched across the circular sound hole - it doesn't have to go through the centre, just connect any two points on the edge.
Quick Tip: Remember that radius is singular, but when talking about multiple radii, the plural form is "radii" - this often trips students up in exams!
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Diameters, Arcs, and Angles
A diameter is basically the biggest chord possible - it's a straight line that goes right through the centre, touching both sides of the circle. Since it's made of two radii joined together, the diameter is always twice as long as the radius.
An arc is simply any curved section of the circle - imagine taking a slice of the circle's edge. There are three types you need to know: minor arcs (less than half the circle), semicircles (exactly half), and major arcs (more than half). It's like cutting a pizza - small slice, half pizza, or most of the pizza!
Central angles are formed when you draw two radii from the centre, creating an angle with its tip right at the centre. These are super important because they help us measure how big an arc is.
Inscribed angles are different - they're formed by two chords meeting at a point on the circle itself, not at the centre. Picture standing on the edge of a circular field and looking at two different points - the angle you're looking through is an inscribed angle.
Memory Trick: Central angles have their vertex at the "central" point (the centre), while inscribed angles are "written on" the circle itself!
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Lines and Circles
When lines interact with circles, they can do so in two main ways, and understanding this difference is crucial for solving geometry problems.
A secant line is like an arrow that shoots straight through the circle, intersecting it at exactly two points. The bit of the secant line between these two intersection points is actually a chord - so every secant line contains a chord within the circle.
A tangent line is much more gentle - it just barely touches the circle at exactly one point, like a ball rolling along a wall. This single touching point is called the point of tangency, and it's special because the tangent line is always perpendicular to the radius at this point.
These concepts might seem simple, but they're the foundation for loads of advanced circle theorems you'll encounter later. Being able to quickly identify whether a line is a secant or tangent will save you tons of time in problem-solving.
Real-world Connection: Think of a bicycle wheel - the spokes are radii, the rim is the circle, and when the wheel touches the ground, that's a tangent line with the ground as the point of tangency!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.9/5
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user