The equations that involve the trigonometric functions of a variable are called trigonometric equations. Trigonometric equation is an equation involving one or more trigonometric ratios of unknown angles. It is expressed as ratios of sine(sin), cosine(cos), tangent(tan), cotangent(cot), secant(sec), cosecant(cosec) angles. For example, cos2 x + 5 sin x = 0 is a trigonometric equation. A function f(x) is said to be periodic if there exists T > 0 such that f(x+T) = f(x) for all x in the domain of definition of f(x). If T is the smallest positive real number such that f(x+T) = f(x), then it is called the period of f(x). All possible values which satisfy the given trigonometric equation are called solutions of the given trigonometric equation.