Book: RD Sharma - Mathematics (Volume 1)
Chapter: 9. Continuity
Subject: Maths - Class 12th
Q. No. 3 of Exercise 9.2
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Find the points of discontinuity, if any, of the following functions :
Basic Idea:
A real function f is said to be continuous at x = c, where c is any point in the domain of f if :
where h is a very small ‘+ve’ no.
i.e. left hand limit as x → c (LHL) = right hand limit as x → c (RHL) = value of function at x = c.
This is very precise, using our fundamental idea of limit from class 11 we can summarise it as, A function is continuous at x = c if :
Here we have,
…Equation 1
Note: [for changing the expression used identity:– (a2–b2) = (a+b)(a–b)]
Note: x – 2 is cancelled from numerator and denominator only because x ≠ 2, else we can’t cancel them
The function is defined for all real numbers, so we need to comment about its continuity for all numbers in its domain ( domain = set of numbers for which f is defined )
Function is changing its nature (or expression) at x = 2, So we need to check its continuity at x = 2 first.
Clearly,
f(2) = 16 [using eqn 1]
Note: (x – 2) is cancelled as x ≠ 2 but x → 2
Clearly, 
∴ f(x) is continuous at x = 2.
Let c be any real number such that c ≠ 0
f(c) = 
[using eqn 1]
Clearly, 
∴ f(x) is continuous for all real x
