Math

Geometry

This is a first year, high-school level course on Geometry (which is based on Euclid's elements). It revisits many of the basic geometrical concepts studied in earlier courses, but addresses them with more mathematical rigor. There is strong focus on proving theorems and results from basic postulates.
Community Questions
A thumbnail for: Points, lines, and planes
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Points, lines, and planes

This topic introduces the basic conceptual tools that underpin our journey through Euclidean geometry. These include the ideas of points, lines, line segments, rays, and planes.
A thumbnail for: Angles and intersecting lines
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Angles and intersecting lines

This topic continues our journey through the world of Euclid by helping us understand angles and how they can relate to each other.
A thumbnail for: Congruent triangles
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Congruent triangles

If you can take one figure and flip, shift and rotate (not resize) it to be identical to another figure, then the two figures are congruent. This topic explores this foundational idea in geometry.
A thumbnail for: Perimeter, area and volume
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Perimeter, area and volume

A broad set of tutorials covering perimeter area and volume with and without algebra.
A thumbnail for: Similarity
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Similarity

A thumbnail for: Right triangles
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Right triangles

Triangles are not always right (although they are never wrong), but when they are it opens up an exciting world of possibilities. Not only are right triangles cool in their own right (pun intended), they are the basis of very important ideas in analytic geometry (the distance between two points in space) and trigonometry.
A thumbnail for: Special properties and parts of triangles
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Special properties and parts of triangles

You probably like triangles. You think they are useful. They show up a lot. What you'll see in this topic is that they are far more magical and mystical than you ever imagined!
A thumbnail for: Quadrilaterals
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Quadrilaterals

Not all things with four sides have to be squares or rectangles! We will now broaden our understanding of quadrilaterals!
A thumbnail for: Circles
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Circles

A thumbnail for: Angles
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Angles

Identifying, measuring, and calculating angles.
A thumbnail for: Triangles
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Triangles

Identifying types of triangles, using principles of similarity and congruence, and applying and proving triangle postulates.
A thumbnail for: Worked Examples
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Worked Examples

Sal does the 80 problems from the released questions from the California Standards Test for Geometry. Basic understanding of Algebra I necessary.