Math Problem Statement

Question 7: Consider the function f(x) = 1/x on the interval [4, 7]. Find the average or mean slope of the function on this interval. By the Mean Value Theorem, we know there exists a c in the open interval (4, 7) such that f'(c) is equal to this mean slope. Find it. Question 8: Consider the function f(x) = 8√x + 2 on the interval [3, 10]. Find the average or mean slope of the function on this interval.

Solution

Let’s break down and solve the problems from your image.


Question 7:

The problem asks:

  1. Find the average or mean slope of the function f(x)=1xf(x) = \frac{1}{x} on the interval [4,7][4, 7].
  2. Find cc in the open interval (4,7)(4, 7) such that f(c)f'(c) equals this mean slope, per the Mean Value Theorem (MVT).

Step 1: Calculate the mean slope

The formula for the mean slope is: Mean slope=f(b)f(a)ba\text{Mean slope} = \frac{f(b) - f(a)}{b - a} Here, a=4a = 4, b=7b = 7, and f(x)=1xf(x) = \frac{1}{x}.

f(4)=14=0.25,f(7)=170.142857f(4) = \frac{1}{4} = 0.25, \quad f(7) = \frac{1}{7} \approx 0.142857

Mean slope=f(7)f(4)74=0.1428570.253=0.10714330.0357\text{Mean slope} = \frac{f(7) - f(4)}{7 - 4} = \frac{0.142857 - 0.25}{3} = \frac{-0.107143}{3} \approx -0.0357


Step 2: Solve for cc using the Mean Value Theorem

The derivative of f(x)f(x) is: f(x)=1x2f'(x) = -\frac{1}{x^2}

Set f(c)=Mean slopef'(c) = \text{Mean slope}: 1c2=0.0357-\frac{1}{c^2} = -0.0357

Simplify: 1c2=0.0357,c2=10.035728.035\frac{1}{c^2} = 0.0357, \quad c^2 = \frac{1}{0.0357} \approx 28.035

c=28.0355.29c = \sqrt{28.035} \approx 5.29

Thus, c5.29c \approx 5.29.


Question 8:

The problem asks:

  1. Find the average or mean slope of the function f(x)=8x+2f(x) = 8\sqrt{x} + 2 on the interval [3,10][3, 10].

Step 1: Calculate the mean slope

The formula for the mean slope is the same: Mean slope=f(b)f(a)ba\text{Mean slope} = \frac{f(b) - f(a)}{b - a}

Here, a=3a = 3, b=10b = 10, and f(x)=8x+2f(x) = 8\sqrt{x} + 2.

f(3)=83+28(1.732)+213.856f(3) = 8\sqrt{3} + 2 \approx 8(1.732) + 2 \approx 13.856 f(10)=810+28(3.162)+227.296f(10) = 8\sqrt{10} + 2 \approx 8(3.162) + 2 \approx 27.296

Mean slope=f(10)f(3)103=27.29613.8567=13.4471.92\text{Mean slope} = \frac{f(10) - f(3)}{10 - 3} = \frac{27.296 - 13.856}{7} = \frac{13.44}{7} \approx 1.92

Thus, the mean slope is approximately 1.921.92.


Step 2: Find cc using the Mean Value Theorem

The derivative of f(x)=8x+2f(x) = 8\sqrt{x} + 2 is: f(x)=82x=4xf'(x) = \frac{8}{2\sqrt{x}} = \frac{4}{\sqrt{x}}

Set f(c)=Mean slopef'(c) = \text{Mean slope}: 4c=1.92\frac{4}{\sqrt{c}} = 1.92

Solve for c\sqrt{c}: c=41.922.083\sqrt{c} = \frac{4}{1.92} \approx 2.083

Square both sides: c(2.083)24.34c \approx (2.083)^2 \approx 4.34

Thus, c4.34c \approx 4.34.


Summary of Results:

  1. Question 7:
    • Mean slope: 0.0357-0.0357
    • c5.29c \approx 5.29
  2. Question 8:
    • Mean slope: 1.921.92
    • c4.34c \approx 4.34

Let me know if you'd like a more detailed explanation or clarification!

Follow-up questions:

  1. How do we interpret the Mean Value Theorem geometrically?
  2. How does the derivative f(c)f'(c) represent the mean slope on the interval?
  3. Could there ever be more than one cc satisfying the Mean Value Theorem?
  4. What happens if a function isn't differentiable on the interval?
  5. Can the Mean Value Theorem apply to non-linear functions?

Tip: Always check the differentiability of the function over the interval when applying the Mean Value Theorem.

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Math Problem Analysis

Mathematical Concepts

Calculus
Average Rate of Change
Mean Value Theorem
Derivatives

Formulas

Mean slope formula: (f(b) - f(a)) / (b - a)
Derivative of 1/x: f'(x) = -1/x²
Derivative of 8√x + 2: f'(x) = 4/√x

Theorems

Mean Value Theorem

Suitable Grade Level

Grades 11-12 (Calculus)