Math Problem Statement

f(x) = ln(x),    [1,8] f it satisfies the hypotheses, find all numbers c that satisfy the conclusion of the Mean Value Theorem

Solution

To solve this problem using the Mean Value Theorem (MVT), we need to verify the hypotheses and then find cc that satisfies the conclusion.

Mean Value Theorem Statement:

If a function f(x)f(x):

  1. is continuous on a closed interval [a,b][a, b],
  2. and differentiable on the open interval (a,b)(a, b),

then there exists a number c(a,b)c \in (a, b) such that: f(c)=f(b)f(a)ba.f'(c) = \frac{f(b) - f(a)}{b - a}.


Step 1: Verify Hypotheses

  1. f(x)=ln(x)f(x) = \ln(x) is continuous on [1,8][1, 8] since ln(x)\ln(x) is continuous for x>0x > 0.
  2. f(x)f(x) is differentiable on (1,8)(1, 8) since the derivative of ln(x)\ln(x) exists and is defined for x>0x > 0.

Thus, f(x)f(x) satisfies the hypotheses of the MVT.


Step 2: Find f(c)f'(c) Using MVT Conclusion

f(c)=f(b)f(a)ba.f'(c) = \frac{f(b) - f(a)}{b - a}. Substitute a=1a = 1, b=8b = 8, and f(x)=ln(x)f(x) = \ln(x): f(8)f(1)81=ln(8)ln(1)7.\frac{f(8) - f(1)}{8 - 1} = \frac{\ln(8) - \ln(1)}{7}. Since ln(1)=0\ln(1) = 0: ln(8)7.\frac{\ln(8)}{7}.

Now, f(c)f'(c) must equal this value: f(c)=ln(8)7.f'(c) = \frac{\ln(8)}{7}.


Step 3: Solve for cc

The derivative of f(x)=ln(x)f(x) = \ln(x) is: f(x)=1x.f'(x) = \frac{1}{x}. So: 1c=ln(8)7.\frac{1}{c} = \frac{\ln(8)}{7}. Solve for cc: c=7ln(8).c = \frac{7}{\ln(8)}.


Final Answer:

The value of cc that satisfies the conclusion of the Mean Value Theorem is: c=7ln(8)where c(1,8).c = \frac{7}{\ln(8)} \quad \text{where } c \in (1, 8).

Would you like me to clarify or expand on any step?


Related Questions:

  1. What are the geometrical implications of the Mean Value Theorem?
  2. How would the solution change if f(x)f(x) were a different logarithmic function, e.g., ln(x+1)\ln(x + 1)?
  3. Can the Mean Value Theorem be applied if f(x)f(x) is discontinuous at one point in the interval?
  4. What happens if cc is outside the interval (1,8)(1, 8)?
  5. What if the interval were changed to [1,e2][1, e^2]? What would cc be?

Tip:

Always check the continuity and differentiability conditions before applying the Mean Value Theorem!

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Math Problem Analysis

Mathematical Concepts

Calculus
Logarithmic Functions
Mean Value Theorem

Formulas

Mean Value Theorem: f'(c) = (f(b) - f(a)) / (b - a)
Derivative of ln(x): f'(x) = 1/x

Theorems

Mean Value Theorem

Suitable Grade Level

Grades 11-12 or early university calculus courses