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Question -

Examine if Rolle’s Theorem isapplicable to any of the following functions. Can you say some thing about theconverse of Rolle’s Theorem from these examples?

(i) 

(ii) 

(iii) 



Answer -

By Rolle’s Theorem, for a function, if

(a) f iscontinuous on [ab]

(b) f isdifferentiable on (ab)

(c) (a)= f (b)

then,there exists some c  (ab)such that 

Therefore, Rolle’s Theorem is notapplicable to those functions that do not satisfy any of the three conditionsof the hypothesis.

(i) 

It is evident that the givenfunction f (x) is not continuous at every integralpoint.

In particular, f(x)is not continuous at = 5 and = 9

 f (x)is not continuous in [5, 9].

The differentiability of f in(5, 9) is checked as follows.

Let be aninteger such that n  (5, 9).

Since the left and right handlimits of f at x = n are notequal, f is not differentiable at x = n

is not differentiable in (5, 9).

It is observed that f doesnot satisfy all the conditions of the hypothesis of Rolle’s Theorem.

Hence,Rolle’s Theorem is not applicable for


(ii) 

It is evident that the givenfunction f (x) is not continuous at every integral point.

In particular, f(x)is not continuous at = −2 and = 2

 f (x) is not continuous in [−2, 2].

The differentiability of f in(−2, 2) is checked as follows.

Let be aninteger such that n  (−2, 2).

Since the left and right handlimits of f at x = n are notequal, f is not differentiable at x = n

is not differentiable in (−2, 2).

It is observed that f doesnot satisfy all the conditions of the hypothesis of Rolle’s Theorem.

Hence,Rolle’s Theorem is not applicable for


(iii) 

It is evident that f,being a polynomial function, is continuous in [1, 2] and is differentiable in(1, 2). 

(1) ≠ f (2)

It is observed that f doesnot satisfy a condition of the hypothesis of Rolle’s Theorem.

Hence,Rolle’s Theorem is not applicable for

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