Any of the functions sine
(sin), cosine (cos), tangent (tan), secant
(sec), cosecant (cosec), or cotangent (cot), or their inverses, sin-1,
etc., which deal with certain proportions in right-angled triangles. For
example, the sine of an angle θ, sin θ, in
a right triangle, is equal to the side opposite the angle divided by the
hypotenuse (the longest side). The plane curve generated by a trigonometric
function is called a trigonometric curve.