The Six Trigonometric Functions
In a right triangle with an angle x, the six trigonometric functions are defined as ratios of the triangle's sides. These functions are fundamental to mathematics, physics, engineering, and many other fields.
Definitions
Sine (sin)
Opposite side divided by the hypotenuse.
sin(x) = opposite / hypotenuse
Cosine (cos)
Adjacent side divided by the hypotenuse.
cos(x) = adjacent / hypotenuse
Tangent (tan)
Opposite side divided by the adjacent side.
tan(x) = opposite / adjacent
Cosecant (csc)
The reciprocal of sine.
csc(x) = 1 / sin(x)
Secant (sec)
The reciprocal of cosine.
sec(x) = 1 / cos(x)
Cotangent (cot)
The reciprocal of tangent.
cot(x) = 1 / tan(x)
Key Identities
- Pythagorean identity: sin²(x) + cos²(x) = 1
- tan(x) = sin(x) / cos(x)
- 1 + tan²(x) = sec²(x)
- 1 + cot²(x) = csc²(x)
Mnemonic: SOH CAH TOA
A popular way to remember the primary trig ratios: Sine = Opposite / Hypotenuse, Cosine = Adjacent / Hypotenuse, Tangent = Opposite / Adjacent.