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Longhand

Chapter 2: Derivatives

The Mean Value Theorem

The Mean Value Theorem says that somewhere on an interval the instantaneous rate equals the average rate. On its own that is a statement about one point; its consequences are what get examined: a function whose derivative is never zero has at most one root, a function whose derivative is bounded cannot grow too fast, and two functions with the same derivative differ by a constant.

This topic is in CLP-1 but not in the current MATH 100 syllabus. It is here for students who want it; it will not be on a test.

Practice questions

Every question below is original material written for Longhand. Open a solution to read the full working, or answer it yourself to have it counted towards your progress.

  • Introductory1 mark · 2 min

    The Mean Value Theorem guarantees a point cc in (1,1)(-1, 1) with f(c)=f(1)f(1)2f'(c) = \dfrac{f(1) - f(-1)}{2} for three of the functions below. For which one does it make no guarantee?

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  • Introductory2 marks · 3 min

    Find the value of cc in (1,4)(1, 4) whose existence the Mean Value Theorem guarantees for f(x)=x2f(x) = x^{2} on [1,4][1, 4].

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  • Introductory1 mark · 2 min

    A car travels 150 km along a highway in exactly 1.5 hours. Its position is a differentiable function of time. According to the Mean Value Theorem, there must be some instant at which the car's speedometer reads exactly what value?

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  • Standard2 marks · 3 min

    Find the point cc promised by the Mean Value Theorem for f(x)=lnxf(x) = \ln x on the interval [1,e][1, e].

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  • Standard3 marks · 5 min

    Let f(x)=x24πx+3sinxf(x) = x^{2} - 4\pi x + 3\sin x. Show that there is a real number cc with f(c)=0f'(c) = 0.

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  • Standard3 marks · 5 min

    How many real roots does the function below have?

    g(x)=4xsin(2x)+1g(x) = 4x - \sin(2x) + 1
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  • Standard2 marks · 3 min

    A function ff satisfies f(x)=3f'(x) = 3 for every real xx, and f(1)=2f(1) = 2. Find f(5)f(5).

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  • Challenging4 marks · 7 min

    Use the Mean Value Theorem to show that 1+x<1+x2\sqrt{1 + x} < 1 + \dfrac{x}{2} for every x>0x > 0.

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  • Challenging3 marks · 6 min

    How many real roots does the function below have?

    p(x)=x44x+1p(x) = x^{4} - 4x + 1
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  • Capstone5 marks · 9 min

    For which values of the constant kk does f(x)=x33x+kf(x) = x^{3} - 3x + k have exactly one real root? Enter the smallest positive integer kk with this property.

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