Definition of sine, cosine, tangent

Thanks to the unit circle we can define sine, cosine and tangent for an arbitrary angle, no longer only for the acute angles of a right triangle. The cosine is the abscissa of the point corresponding to the angle, the sine is its ordinate, the tangent their ratio. From this definition follow the fundamental identity and the properties of domain, range and sign.

• Sine, cosine and tangent of an arbitrary angle
• The fundamental identity
• Domain, range and sign