Proving the Mean Value Theorem with 3 ≤ f'(x) ≤ 5: A Homework Help Guide

In summary, the mean-value theorem states that there exists some c in the interval (2,8) where f'(c) is equal to the average rate of change of f(x) between x=2 and x=8. Using this, we can show that 18≤ f(8) - f(2) ≤30 by multiplying the given inequality by 6.
  • #1
Loppyfoot
194
0

Homework Statement


Let us suppose that, 3≤ f '(x) ≤5 for all x values. Show that 18≤ f(8) - f(2) ≤30.


The Attempt at a Solution


Alright folks... I am unsure where to start, or where to apply the MVT or the Rolle's Theorem.

Thanks
 
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  • #2
Well the mean-value theorem states that you can find some c in the interval (2,8) such that:
[tex]f'(c) = \frac{f(8)-f(2)}{8-2}[/tex]
Now just note:
[tex]3 \leq f'(c)=\frac{f(8)-f(2)}{8-2} \leq 5[/tex]
 
  • #3
Alright, I understand that that is the equation of the secant line. How do I prove that it is ≤18 and ≤30?
 
  • #4
You have:
[tex]3 \leq \frac{f(8)-f(2)}{6}\leq 5[/tex]
by my previous post. Multiplying by 6 you get:
[tex]3\times 6 \leq f(8)-f(2)\leq 5\times 6[/tex]
 
  • #5
Oh... silly me. You multiply the six out of the bottom.
Thanks man, that really helped. Much love brah.
 

1. What is the Mean Value Theorem?

The Mean Value Theorem is a fundamental theorem in calculus that states that if a function is continuous on a closed interval and differentiable on the open interval, then there exists a point within the interval where the slope of the tangent line is equal to the average rate of change of the function over that interval.

2. How is the Mean Value Theorem used in calculus?

The Mean Value Theorem is used to prove a variety of important theorems in calculus, such as the first and second derivative tests for finding extrema, the intermediate value theorem, and the fundamental theorem of calculus. It is also used to solve optimization problems and to prove the convergence of certain series.

3. What is the significance of 3 ≤ f'(x) ≤ 5 in the Mean Value Theorem?

3 ≤ f'(x) ≤ 5 is a condition that must be met in order for the Mean Value Theorem to be applied. This condition ensures that the function is both continuous and differentiable on the given interval. If this condition is not met, then the Mean Value Theorem cannot be used to prove the existence of a point with a specific slope.

4. How is the Mean Value Theorem proven with 3 ≤ f'(x) ≤ 5?

The Mean Value Theorem can be proven using a combination of the Intermediate Value Theorem and Rolle's Theorem. First, the Intermediate Value Theorem is used to show that the function must take on the average rate of change at some point within the interval. Then, Rolle's Theorem is used to show that there must be a point where the derivative is equal to the average rate of change, thus proving the Mean Value Theorem.

5. Can the Mean Value Theorem be applied to all functions?

No, the Mean Value Theorem only applies to continuous functions that are differentiable on a closed interval. If a function is not continuous or differentiable, then the Mean Value Theorem cannot be used. Additionally, if the given interval does not satisfy the condition of 3 ≤ f'(x) ≤ 5, then the Mean Value Theorem cannot be applied.

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