A function f(x) is said to be continuous, if it is continuous at each point of its domain.**Everywhere continuous function**: A function f(x) is said to be everywhere continuous if it is continuous on the entire real line (-∞, ∞) i.e. On R.

**Some fundamental results on continuous functions: **Here, we list some fundamentals result on continuous functions without giving their proofs.

**Result: ** Let f (x) and g(x) be two continuous functions on their common domain D and let c be real number. Then

- C f is continuous
- f + g is continuous
- f – g is continuous
- fg is continuous
- f/g is continuous
- f
^{n}, for all n ϵ N is continuous.

**Result: **Listed below are some common type of functions that are continuous in their domains.

** Constant function**: Every constant function is every – where continuous.

** Identity function**: The identity function I(x) is defined by I(x) = x for all x ϵ R

** Modulus function**: The modulus function f (x) is defined as \(f\left( x \right)=\left| x \right|=\left\{ \begin{align} & x,\,\,\,\,\,\,\,\,if\,\,x\ge 0 \\ & -x,\,\,\,\,if\,\,x<0 \\\end{align} \right.\) clearly, the domain of f(x) is R and this function is everywhere continuous.

** Exponential function**: if a is positive real number, other than unity, then the function f(x) defined by f(x) = a^{x} for all x ϵ R is called the exponential function. The domain of this function id R. it is evident form its graph that it everywhere continuous.

** Logarithm function**: if a is positive real number other than unity, then a function by f(x) = log_{a} x is called the logarithm function. Clearly its domain is the set of all positive real numbers and it is continuous on its domain.

** Polynomial function**: A function of the form f (x) = a_{0} + a_{1}x + a_{2}x + … + a_{n }x^{n}, where a_{0}, a_{1}, a_{2}, … a_{n} ϵ R is called a polynomial function. This function is everywhere continuous.

** Rational function**: if p(x) and q(x) are two polynomials, then a function, f(x) of the form f(x) = p(x)/ q(x), q(x) ≠ 0 is called a polynomial function. This function is continuous on its domain i.e., it is everywhere continuous except at points where q(x) = 0.

** Trigonometric functions**: all trigonometrical functions viz. sin x, cos x, tan x, cosec x, cot x are continuous at each point of their respective domains.

**Result: **The composition of two continuous functions is a continuous function i.e., f and g are two functions such that g is continuous at a point a and f is continuous at g (a), then fog continuous at a.