Trigonometric function, in mathematics, one of six functions (sine, cosine, tangent, cotangent, secant, and cosecant) that represent ratios of sides of right triangles. They are also known as the circular functions since their values can be defined as ratios of the x and y coordinates (see coordinate system) of points on a circle of radius 1 that correspond to angles in standard positions. Such values have been tabulated and programmed into scientific calculators and computers. We’ve used the unit circle to define the trigonometric functions for acute angles so far. We’ll need more than acute angles in the next section where we’ll look at oblique triangles. Some oblique triangles are obtuse, and we’ll need to know the sine and cosine of obtuse angles. As long as we’re doing that, we should also define the trig functions for angles beyond 180° and negative angles.