Math is Fun - Trigonometry
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Illustrated introduction to right-triangle trigonometry from the Math is Fun site. It defines sine, cosine and tangent as side ratios, introduces the unit circle and common angles, and works simple examples so learners can find missing sides and angles in triangles.
More resources on Trigonometric Functions
Wolfram MathWorld
MathWorld is an online mathematics encyclopedia from Wolfram Research offering detailed, browsable articles on topics across the math spectrum, including algebra, geometry, calculus, and number theory. Each entry includes definitions, theorems, formulas, diagrams, worked examples, and links to further reading.
Paul's Online Math Notes - Trig
Review section from Paul Dawkins' Calculus I notes at Lamar University. It recaps radians, the unit circle, the six trig functions, their graphs and periodicity, and evaluating them at standard angles, with worked examples that prepare learners for trigonometry inside calculus.
Trigonometry Khan Academy
Master law of sines & cosines with Sal Khan's free Trigonometry course! Ace triangles & trigonometry calculations.
Trigonometry
A short, problem-driven text from the Gelfand School Outreach Program that builds trigonometric functions from geometry, then treats them as functions in their own right. Readers learn addition formulas, identities, and graphs and come away prepared for calculus.
mathsisfun.com
MathIsFun.com is a beginner-friendly math site that explains concepts with clear, step-by-step lessons and interactive activities. It covers topics from algebra and linear equations to geometry, fractions, data, and more, with practice problems, worksheets, and quizzes.