The functions sine, cosine and tangent of an angle are sometimes referred to as the primary or basic trigonometric functions.
The remaining trigonometric functions secant (sec), cosecant (csc), and cotangent (cot) are defined as the reciprocal functions of cosine, sine, and tangent, respectively.
Trigonometric identities are equations involving the trigonometric functions that are true for every value of the variables involved
Each of the six trig functions is equal to its co-function evaluated at the complementary angle.
The Trigonometric Identities are equations that are true for Right Angled Triangles
Periodicity of trig functions. Sine, cosine, secant, and cosecant have period 2π while tangent and cotangent have period π. Identities for negative angles
Sine, tangent, cotangent, and cosecant are odd functions while cosine and secant are even functions.