Goniometric function

α = angle between line segments AB and AC

The goniometric functions sinus (sin), cosinus (cos), tangent (tan), cotangent (cot), secant (sec), and cosecant (cst) relate an angle of a right-angled triangle to ratios of two side lengths.

The most common convention is to name the inverse functions using the prefix "arc".

	sin(α) = BC / AB	α = arcsin(BC / AB)
	cos(α) = AC / AB	α = arccos(AC / AB)
	tan(α) = BC / AC	α = arctan(BC / AC)
	cot(α) = AC / BC	α = arccot(AC / BC)
	sec(α) = AB / AC	α = arcsec(AB / AC)
	csc(α) = AB / BC	α = arccsc(AB / BC)

	sin(α) = cos(90° - α)	tan(α) = cot^-1(α)
	sin(α) = -sin(180° - α)	tan(α) = cot(90° - α)
	sin(α)² + cos(α)² = 1	tan(α) = -tan(180° - α)
		tan(α)² + 1 = cos(α)^-2
		cot(α)² + 1 = sin(α)^-2

Last modified:27 December 2025 10.12 a.m.

View this page in: Nederlands