Calculus/Rolle's Theorem

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Rolle's Theorem
Rolle's Theorem

If a function, , is continuous on the closed interval , is differentiable on the open interval , and , then there exists at least one number c, in the interval such that

Rolle's Theorem is important in proving the Mean Value Theorem.

Examples[edit | edit source]

Rolle's theorem.svg


. Show that Rolle's Theorem holds true somewhere within this function. To do so, evaluate the x-intercepts and use those points as your interval.


1: The question wishes for us to use the x-intercepts as the endpoints of our interval.

Factor the expression to obtain . x = 0 and x = 3 are our two endpoints. We know that f(0) and f(3) are the same, thus that satisfies the first part of Rolle's theorem (f(a) = f(b)).

2: Now by Rolle's Theorem, we know that somewhere between these points, the slope will be zero. Where? Easy: Take the derivative.

Thus, at , we have a spot with a slope of zero. We know that (or 1.5) is between 0 and 3. Thus, Rolle's Theorem is true for this (as it is for all cases). This was merely a demonstration.