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# High school geometry

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Pythagorean theorem: Right triangles & trigonometryPythagorean theorem proofs: Right triangles & trigonometrySpecial right triangles: Right triangles & trigonometryIntroduction to the trigonometric ratios: Right triangles & trigonometrySolving for a side in a right triangle using the trigonometric ratios: Right triangles & trigonometrySolving for an angle in a right triangle using the trigonometric ratios: Right triangles & trigonometry

Modeling with right triangles: Right triangles & trigonometryTrigonometric ratios & similarity: Right triangles & trigonometrySine & cosine of complementary angles: Right triangles & trigonometryLaw of sines: Right triangles & trigonometryLaw of cosines: Right triangles & trigonometrySolving general triangles: Right triangles & trigonometry

Circle basics: CirclesArc measure: CirclesArc length (from degrees): CirclesIntroduction to radians: CirclesArc length (from radians): CirclesSectors: CirclesInscribed angles: Circles

Inscribed shapes problem solving: CirclesProperties of tangents: CirclesGraphs of circles intro: CirclesStandard equation of a circle: CirclesExpanded equation of a circle: CirclesConstructing regular polygons inscribed in circles: CirclesConstructing circumcircles & incircles: CirclesConstructing a line tangent to a circle: Circles

Test your knowledge of the skills in this course. Have a test coming up? The Course challenge can help you understand what you need to review.

## Review articles

## Get StartedIntro to Euclidean geometry

Roughly 2400 years ago, Euclid of Alexandria wrote Elements which served as the world's geometry textbook until recently. Studied by Abraham Lincoln in order to sharpen his mind and truly appreciate mathematical deduction, it is still the basis of what we consider a first year course in geometry.
This tutorial gives a bit of this background and then lays the conceptual foundation of points, lines, circles and planes that we will use as we journey through the world of Euclid.

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