Continuous function

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

(i)                  C f is continuous

(ii)                f + g is continuous

(iii)               f - g is continuous

(iv)              fg is continuous

(v)                f/g is continuous

(vi)              fⁿ, for all n ϵ N is continuous.

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

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

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

c. Modulus function: The modulus function f (x) is defined as clearly, the domain of f(x) is R and this function is everywhere continuous.

d. 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.

e. 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.

f. Polynomial function: A function of the form f (x) = a₀ + a₁x + a₂x + … + a_n xⁿ, where a₀, a₁, a₂,… a_n ϵ R is called a polynomial function. This function is everywhere continuous.

g. 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.

h. 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.