The unit circle definition of sine, cosine, and tangent

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Radians & degrees
Trig values of special angles
Use the Pythagorean identity

Learn about radians, which are the official unit of measurement for angles in algebra (in contrast to degrees, which are used in geometry).

Learn about the ingenious way in which we define the trigonometric functions for any real number.

Learn how the graphs of y=sin(θ), y=cos(θ), and y=tan(θ) look, using the unit circle definition of the functions.

Learn about very useful trigonometric identities that arise by considering different properties of the unit circle definition.

Learn how to find the trigonometric values of some special angles without the use of a calculator.

Watch videos by Sal and Vi that discuss the ongoing battle between the more popular Pi (π=3.14..) and its more qualified rival Tau (τ=6.28...).