Question Details

Rolle’s theorem is a special case of

Options

A

Euclid’s theorem

B

another form of Rolle’s theorem

C

Lagrange’s mean value theorem

D

Joule’s theorem

Correct Answer :

Lagrange’s mean value theorem

Solution :

The correct option is Lagrange’s mean value theorem.

To understand why Rolle's theorem is a special case of Lagrange's Mean Value Theorem (LMVT), let us analyze the statements of both theorems.

Lagrange’s Mean Value Theorem:
If a function f(x) is:
1. Continuous on the closed interval [a,b], and
2. Differentiable on the open interval (a,b),
then there exists at least one point c in the open interval (a,b) such that:

f(c) = f(b) - f(a) b - a

This formula represents the slope of the tangent line at x=c being equal to the slope of the secant line passing through the endpoints (a,f(a)) and (b,f(b)).

Rolle’s Theorem:
Rolle's theorem adds a third specific condition to the first two:
3. The function values at the endpoints are equal, i.e., f(a)=f(b).

If we apply this special condition f(a)=f(b) to the equation in Lagrange's Mean Value Theorem, we get:

f(c) = f(b) - f(b) b - a = 0

Thus, f(c)=0, which is the exact conclusion of Rolle’s theorem.

Therefore, Rolle's theorem is a specific case of Lagrange's Mean Value Theorem where the secant line is horizontal (slope is zero).

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