Learn about circles, their properties, and related theorems with interactive exercises and videos on Khan Academy.

Explore geometry concepts related to circles, including properties, formulas, and applications, through engaging lessons and exercises on Khan Academy.

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Given the graph of a circle or its features, find its standard equation. Skip to main content If you're seeing this message, it means we're having trouble loading external resources on our website.

The circle is arguably the most fundamental shape in our universe, whether you look at the shapes of orbits of planets, whether you look at wheels, whether you look at things on kind of …

Drawing a number line helps visualize 'x is less than 4'. We mark 4 with a circle, not a dot, because 4 isn't included. Then, we color the line below 4, showing all values less than 4. Easy …

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Sal constructs a circle that circumscribes a given triangle using compass and straightedge. Created by Sal Khan.

Learn trigonometry—right triangles, the unit circle, graphs, identities, and more.