Kruh a kružnica sú všade okolo nás - od kolies... Show more
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Updated Mar 30, 2026
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Kruh a Kružnica: Vlastnosti a Polohy
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Kruh vs. Kružnica - Základné pojmy
Prvá vec, ktorú si musíš zapamätať: kružnica nie je to isté ako kruh! Kružnica je len čiara (obvod), zatiaľ čo kruh je celá plocha vrátane vnútra.
Kružnica je množina všetkých bodov, ktoré majú rovnakú vzdialenosť od stredu. Kruh obsahuje aj všetky body vo vnútri tejto čiary. Predstav si to takto: drôt ohnutý do kruhu je kružnica, ale minca je kruh.
Kľúčové pojmy, ktoré budeš potrebovať: polomer (r) je vzdialenosť od stredu k okraju, priemer (d) je najdlhšia úsečka cez stred . Tetiva spája dva body na kružnici, oblúk je časť kružnice medzi dvoma bodmi.
💡 Tip: Nezamieňaj polomer a priemer! Priemer je vždy dvakrát väčší ako polomer.
Vzorce pre obvod a obsah
Dva najdôležitejšie vzorce, ktoré sa ti budú hodiť na testoch: obvod kružnice = 2πr a obsah kruhu = πr².
Pre výpočty používaj π ≈ 3,14 (ak nie je zadané inak). Pamätaj si jednotky - obvod meráš v cm alebo m, obsah v cm² alebo m².
Ak máš zadaný priemer namiesto polomeru, jednoducho ho vydeľ dvoma. Alebo použij vzorec o = πd pre obvod.
Príklad: Pri polomere 5 cm je obvod = 2 × 3,14 × 5 = 31,4 cm a obsah = 3,14 × 5² = 78,5 cm².
💡 Skúška: Obsah je vždy v štvorcových jednotkách, obvod v lineárnych!
Priamka a kružnica - tri možnosti
Keď sa priamka stretne s kružnicou, môže sa stať jedna z troch vecí. Závisí to od vzdialenosti (v) stredu kružnice od priamky.
Sečnica (v < r): Priamka pretína kružnicu v dvoch bodoch. Dotyčnica : Priamka sa dotýka kružnice len v jednom bode a je kolmá na polomer v tomto bode. Nesečnica (v > r): Priamka sa kružnice vôbec nedotýka.
Najdôležitejšie si zapamätaj: dotyčnica je vždy kolmá na polomer v bode dotyku! Toto ti pomôže pri riešení úloh s pravouhlými trojuholníkmi.
💡 Vizuálna pomôcka: Nakresli si obrázok - lepšie si to zapamätáš!
Uhly v kružnici
V kružnici rozlišujeme dva typy uhlov. Stredový uhol má vrchol v strede kružnice, obvodový uhol má vrchol na kružnici.
Tu je kľúčový vzťah: obvodový uhol je vždy polovičkou stredového uhla, ak prislúchajú k rovnakému oblúku. Takže α = ω/2.
Thalesova kružnica je špeciálny prípad - ak je obvodový uhol nad priemerom, je vždy 90°. Toto pravidlo sa ti bude hodiť pri konštrukciách.
Príklad: Stredový uhol 120° znamená obvodový uhol 60°.
💡 Pamätaj: Všetky obvodové uhly nad tým istým oblúkom sú rovnaké!
Praktické tipy na testy
Pri riešení úloh si vždy najprv zapíš, čo vieš a čo hľadáš. Nezabudni na jednotky a skontroluj, či máš polomer alebo priemer.
Ak vidíš úlohu s dotyčnicou, hneď si nakreslí pravý uhol medzi dotyčnicou a polomerom. Pri uhloch v kružnici si označ, ktorý je stredový a ktorý obvodový.
Časté chyby: Zamieňanie polomeru s priemerom, nesprávne jednotky pri obsahu, zabúdanie na pravidlo o dotyčnici. Výsledok môžeš nechať aj s π, ak to zadanie nevyžaduje číselnú hodnotu.
💡 Kontrola: Obsah kruhu by mal byť väčší ako obsah štvorca s rovnakou stranou ako polomer!
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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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. 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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. 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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Kruh a Kružnica: Vlastnosti a Polohy
Kruh a kružnica sú všade okolo nás - od kolies bicyklov až po mince v peňaženke. Pochopenie týchto základných geometrických tvarov ti pomôže nielen v matematike, ale aj vo fyzike a technike.
Kruh vs. Kružnica - Základné pojmy
Prvá vec, ktorú si musíš zapamätať: kružnica nie je to isté ako kruh! Kružnica je len čiara (obvod), zatiaľ čo kruh je celá plocha vrátane vnútra.
Kružnica je množina všetkých bodov, ktoré majú rovnakú vzdialenosť od stredu. Kruh obsahuje aj všetky body vo vnútri tejto čiary. Predstav si to takto: drôt ohnutý do kruhu je kružnica, ale minca je kruh.
Kľúčové pojmy, ktoré budeš potrebovať: polomer (r) je vzdialenosť od stredu k okraju, priemer (d) je najdlhšia úsečka cez stred . Tetiva spája dva body na kružnici, oblúk je časť kružnice medzi dvoma bodmi.
💡 Tip: Nezamieňaj polomer a priemer! Priemer je vždy dvakrát väčší ako polomer.
Sign up to see the contentIt's free!
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Vzorce pre obvod a obsah
Dva najdôležitejšie vzorce, ktoré sa ti budú hodiť na testoch: obvod kružnice = 2πr a obsah kruhu = πr².
Pre výpočty používaj π ≈ 3,14 (ak nie je zadané inak). Pamätaj si jednotky - obvod meráš v cm alebo m, obsah v cm² alebo m².
Ak máš zadaný priemer namiesto polomeru, jednoducho ho vydeľ dvoma. Alebo použij vzorec o = πd pre obvod.
Príklad: Pri polomere 5 cm je obvod = 2 × 3,14 × 5 = 31,4 cm a obsah = 3,14 × 5² = 78,5 cm².
💡 Skúška: Obsah je vždy v štvorcových jednotkách, obvod v lineárnych!
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Priamka a kružnica - tri možnosti
Keď sa priamka stretne s kružnicou, môže sa stať jedna z troch vecí. Závisí to od vzdialenosti (v) stredu kružnice od priamky.
Sečnica (v < r): Priamka pretína kružnicu v dvoch bodoch. Dotyčnica : Priamka sa dotýka kružnice len v jednom bode a je kolmá na polomer v tomto bode. Nesečnica (v > r): Priamka sa kružnice vôbec nedotýka.
Najdôležitejšie si zapamätaj: dotyčnica je vždy kolmá na polomer v bode dotyku! Toto ti pomôže pri riešení úloh s pravouhlými trojuholníkmi.
💡 Vizuálna pomôcka: Nakresli si obrázok - lepšie si to zapamätáš!
Sign up to see the contentIt's free!
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Improve your grades
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Uhly v kružnici
V kružnici rozlišujeme dva typy uhlov. Stredový uhol má vrchol v strede kružnice, obvodový uhol má vrchol na kružnici.
Tu je kľúčový vzťah: obvodový uhol je vždy polovičkou stredového uhla, ak prislúchajú k rovnakému oblúku. Takže α = ω/2.
Thalesova kružnica je špeciálny prípad - ak je obvodový uhol nad priemerom, je vždy 90°. Toto pravidlo sa ti bude hodiť pri konštrukciách.
Príklad: Stredový uhol 120° znamená obvodový uhol 60°.
💡 Pamätaj: Všetky obvodové uhly nad tým istým oblúkom sú rovnaké!
Sign up to see the contentIt's free!
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Improve your grades
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Praktické tipy na testy
Pri riešení úloh si vždy najprv zapíš, čo vieš a čo hľadáš. Nezabudni na jednotky a skontroluj, či máš polomer alebo priemer.
Ak vidíš úlohu s dotyčnicou, hneď si nakreslí pravý uhol medzi dotyčnicou a polomerom. Pri uhloch v kružnici si označ, ktorý je stredový a ktorý obvodový.
Časté chyby: Zamieňanie polomeru s priemerom, nesprávne jednotky pri obsahu, zabúdanie na pravidlo o dotyčnici. Výsledok môžeš nechať aj s π, ak to zadanie nevyžaduje číselnú hodnotu.
💡 Kontrola: Obsah kruhu by mal byť väčší ako obsah štvorca s rovnakou stranou ako polomer!
Sign up to see the contentIt's free!
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Improve your grades
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Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and 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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Students love us — and so will you.
4.6/5
App Store
4.7/5
Google Play
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. 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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. 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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user