Sine, Cosine, and Tangent are all functions of an angle, which are useful in right triangle calculations. For an angle designated as θ, the sine function is abbreviated as sin θ, the cosine function is abbreviated as cos θ, and the tangent function is abbreviated as tan θ. For any angle θ, sin θ, cos θ, and tan θ are each single determined values and if θ is a known value, sin θ, cos θ, and tan θ may be looked up in a table or determined with a calculator.

These three functions are related to right triangles in the following ways:

• Sine of a non-right angle equals the length of the leg opposite that angle divided by the length of the hypotenuse.

• Cosine of a non-right angle equals the length of the leg adjacent to it divided by the length of the hypotenuse.

• Tangent of a non-right angle equals the length of the leg opposite that angle divided by the length of the leg adjacent to it.

Any trigonometric expression can be written in terms of sines and cosines.  The graphs of sin θ (red color) and cos θ  (green color) for −2π ≤ θ ≤ 2π are depicted below: