## What’s the equator? Geography and the Earth

This globe shows the equator running around the widest part of the Earth. Where is the equator? The equator is an imaginary line running around the widest part of the Earth, [...]

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08, 2017

This globe shows the equator running around the widest part of the Earth. Where is the equator? The equator is an imaginary line running around the widest part of the Earth, [...]

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07, 2017

This is a sphere. A sphere is a three-dimensional circle. Or you could say that a sphere is the set of all the points that are at the same distance from the center [...]

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07, 2017

What is a radius? The geometry of a circle What is a radius? The radius of a circle is the distance from the center point to the edge of the circle. It's the same [...]

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07, 2017

What is pi? The geometry of a circle What is pi? Pi is a number that is just a little bigger than 3.14. It is the number you get if you divide [...]

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07, 2017

This is a cylinder. What can you find around your house that's a cylinder? A cylinder is a circle moved through space to make a solid form. The ends are circles that [...]

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07, 2017

The geometry of a circle, with circumference labelled What is the circumference? The circumference of a circle is the distance all the way around the circle. It's the same as the perimeter, but [...]

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07, 2017

Proof for the area of a circle: Divide a circle up into sections like an orange Euclid's proof We know it's true that A=πr-squared is the area of a circle, but how can we prove [...]

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07, 2017

A circle is the set of points on a plane that are all the same distance away from a center point. A circle is the set of points on a plane that are all [...]

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07, 2017

The geometry of a circle The area of a circle is the flat surface inside its circumference. The area is always equal to the radius squared, multiplied by π (pi). Here's a proof that [...]

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07, 2017

Greek mathematics: An Egyptian papyrus from about 100 AD which is a piece of one of Euclid's books Greek math: geometry not algebra Because people in ancient Greece had only very clumsy [...]