Is the function defined by
\[f(x) = \begin{cases} x+5, & \quad \text{if } x{\leq 1}\\ x-5, & \quad \text{if } x \text{>1} \end{cases}\]a continuous function?
Is the function defined by
\[f(x) = \begin{cases} x+5, & \quad \text{if } x{\leq 1}\\ x-5, & \quad \text{if } x \text{>1} \end{cases}\]a continuous function?
Solution and Explanation
The given function is
\(f(x) = \begin{cases} x+5, & \quad \text{if } x{\leq 1}\\ x-5, & \quad \text{if } x \text{>1} \end{cases}\)
The given function f is defined at all the points of the real line.
Let c be a point on the real line.
Case (i):
If c<1, then f(c) = c+5 and \(\lim\limits_{x \to c}\) f(x) = \(\lim\limits_{x \to c}\) f(x+5) = c+5
∴\(\lim\limits_{x \to c}\) f(x) = f(c)
Therefore, f is continuous at all points x, such that x<1
Case (ii):
If c = 1, then f(1) = 1+5 = 6
The left hand limit of f at x = 1 is
\(\lim\limits_{x \to 1^-}\)f(x) = \(\lim\limits_{x \to 1^-}\)(x+5) = 1+5 = 6
The right hand limit of f at x = 1 is,
\(\lim\limits_{x \to 1^+}\)f(x) = \(\lim\limits_{x \to 1^+}\)(x-5) = 1-5 = -4
It is observed that the left and right hand limit of f at x=1 do not coincide.
Therefore,f is not continuous at x=1
Case(III):
Ifc>1, then f(c) = c-5 and
\(\lim\limits_{x \to c}\) f(x) = \(\lim\limits_{x \to c}\) (x-5) = c-5
∴\(\lim\limits_{x \to c}\) f(x) = f(c)
Therefore, f is continuous at all points x, such that x>1
Thus, from the above observation, it can be concluded that x=1 is the only point of discontinuity of f.
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Notes on Continuity and differentiability
Concepts Used:
Continuity
A function is said to be continuous at a point x = a, if
limx→a
f(x) Exists, and
limx→a
f(x) = f(a)
It implies that if the left hand limit (L.H.L), right hand limit (R.H.L) and the value of the function at x=a exists and these parameters are equal to each other, then the function f is said to be continuous at x=a.
If the function is undefined or does not exist, then we say that the function is discontinuous.
Conditions for continuity of a function: For any function to be continuous, it must meet the following conditions:
- The function f(x) specified at x = a, is continuous only if f(a) belongs to real number.
- The limit of the function as x approaches a, exists.
- The limit of the function as x approaches a, must be equal to the function value at x = a.