MathsIsFun Unit Circle
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A Math Is Fun page introducing the unit circle with an interactive diagram showing how sine, cosine and tangent correspond to lengths as the angle changes. Learners understand where the trigonometric ratios come from and how their signs vary by quadrant.
More resources on Unit Circle
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.
Trigonometry Khan Academy
Master law of sines & cosines with Sal Khan's free Trigonometry course! Ace triangles & trigonometry calculations.
Trigonometry Fundamentals — Lockdown Live Math Ep. 2
Grant Sanderson's 73-minute live lecture deriving trigonometry from the unit circle: why sine and cosine are coordinates, where the Pythagorean identity comes from, negative angles, and the half-angle formula, with live audience problems throughout. It derives the unit-circle definitions rather than presenting them as a table to memorize, and the accompanying lesson page at 3blue1brown.com carries the notes and practice problems. F
OpenStax Algebra and Trigonometry 2e — 7.3 Unit Circle
Section 7.3 of OpenStax's peer-reviewed open textbook redefines sine and cosine via the unit circle. Covers special angles of 30, 45, and 60 degrees, domain and range, reference angles, and the Pythagorean identity, with worked examples.
Khan Academy: The Unit Circle Definition of Sine, Cosine, and Tangent
Free unit from Khan Academy's trigonometry course extending sine, cosine, and tangent from right triangles to the full unit circle. Includes video lessons, radian conversion, Pythagorean identity work, and graded practice exercises with instant feedback. It actually builds the unit-circle definition from right-triangle trig and tests retention with exercises.
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.