Theorems of Calculus in Practice - Case Studies

Example

Case Study 1: The Extreme Value Theorem in Material Optimization
When designing a cylindrical water storage tank, an engineer is tasked with maximizing the volume for a fixed amount of surface area (representing material cost). The volume function V(r)V(r) is defined for the radius rr on a closed interval [rmin,rmax][r_{min}, r_{max}], dictated by physical site constraints. Because V(r)V(r) is a continuous polynomial function on a closed interval, the Extreme Value Theorem (EVT) guarantees that an absolute maximum volume must exist. The engineer knows they only need to check the critical points where V(r)=0V'(r)=0 and the boundary endpoints rminr_{min} and rmaxr_{max} to find the optimal design.

Example

Case Study 2: The Mean Value Theorem and Highway Speed Enforcement
Automated toll systems on tollways record the exact time a vehicle enters and exits the highway. If the distance between two toll booths is 120 kilometers, and a driver completes the journey in exactly 1 hour, their average speed is 120 km/h. If the posted speed limit is 100 km/h, the Mean Value Theorem (MVT) provides mathematical proof that at least one specific instant during that hour, the driver's exact speedometer reading (instantaneous velocity) was exactly 120 km/h. Law enforcement agencies use this principle for point-to-point average speed cameras.

The Extreme Value Theorem (EVT) - Examples

Example

Find the absolute maximum and minimum values of the function f(x)=x33x2+1f(x) = x^3 - 3x^2 + 1 on the closed interval [1/2,4][-1/2, 4].

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Example

Find the absolute extrema of f(x)=x2sinxf(x) = x - 2\sin x on the interval [0,2π][0, 2\pi].

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Example

Why does the Extreme Value Theorem fail for f(x)=1/xf(x) = 1/x on the interval [1,1][-1, 1]?

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Rolle's Theorem - Examples

Example

Verify Rolle's Theorem for the function f(x)=x24x+3f(x) = x^2 - 4x + 3 on the interval [1,3][1, 3].

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Example

Verify Rolle's Theorem for f(x)=sinxf(x) = \sin x on the interval [0,π][0, \pi].

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Example

Why does Rolle's Theorem fail for f(x)=xf(x) = |x| on the interval [1,1][-1, 1]?

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The Mean Value Theorem (MVT) - Examples

Example

Apply the Mean Value Theorem to the function f(x)=x3xf(x) = x^3 - x on the interval [0,2][0, 2].

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Apply the MVT to the function f(x)=ln(x)f(x) = \ln(x) on the interval [1,e][1, e].

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Show that the equation x5+10x+3=0x^5 + 10x + 3 = 0 has exactly one real root using Rolle's Theorem and IVT.

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Cauchy's Mean Value Theorem - Examples

Example

Verify Cauchy's Mean Value Theorem for the functions f(x)=x2f(x) = x^2 and g(x)=x3g(x) = x^3 on the interval [1,2][1, 2].

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Example

Use Cauchy's Mean Value Theorem to prove the first step of L'Hopital's Rule for limits resulting in 0/00/0.

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