Math Problem Statement

Suppose that f(x) = (x^2 + A) / x, where A is a constant. If f''(2) = 1/8, find the value of A.

Solution

We are given the function f(x)=x2+Axf(x) = \frac{x^2 + A}{x}, where AA is a constant. We also know that f(2)=18f''(2) = \frac{1}{8}, and we need to find the value of AA.

Step 1: Differentiate f(x)f(x)

Let's start by simplifying the given function: f(x)=x2+Ax=x+Axf(x) = \frac{x^2 + A}{x} = x + \frac{A}{x}

Now, we will differentiate f(x)f(x) to find f(x)f'(x) and then f(x)f''(x).

First derivative f(x)f'(x):

f(x)=ddx(x+Ax)f'(x) = \frac{d}{dx}\left(x + \frac{A}{x}\right) Using the power rule: f(x)=1Ax2f'(x) = 1 - \frac{A}{x^2}

Second derivative f(x)f''(x):

Now, differentiate f(x)f'(x): f(x)=ddx(1Ax2)f''(x) = \frac{d}{dx}\left(1 - \frac{A}{x^2}\right) f(x)=0+2Ax3=2Ax3f''(x) = 0 + \frac{2A}{x^3} = \frac{2A}{x^3}

Step 2: Use the given condition f(2)=18f''(2) = \frac{1}{8}

We are told that f(2)=18f''(2) = \frac{1}{8}, so substitute x=2x = 2 into the expression for f(x)f''(x): f(2)=2A23=2A8=A4f''(2) = \frac{2A}{2^3} = \frac{2A}{8} = \frac{A}{4} Set this equal to the given value 18\frac{1}{8}: A4=18\frac{A}{4} = \frac{1}{8}

Step 3: Solve for AA

To solve for AA, multiply both sides by 4: A=48=12A = \frac{4}{8} = \frac{1}{2}

Thus, the value of AA is 12\frac{1}{2}.

Final Answer:

A=12A = \frac{1}{2}

Would you like more details on any step, or do you have further questions?


Here are 5 related questions to explore:

  1. How would you differentiate a function involving higher powers of xx and constants, like x3+Bx\frac{x^3 + B}{x}?
  2. Can you solve a similar problem where the given second derivative is 14\frac{1}{4}?
  3. How do we apply the chain rule when differentiating more complex functions?
  4. What would happen if AA were a function of xx instead of a constant?
  5. How would the solution change if you were asked to find f(3)f'(3) instead?

Tip: When solving calculus problems, always simplify functions as much as possible before differentiating—it makes the process quicker and reduces errors.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Second Derivative
Algebraic Manipulation

Formulas

f'(x) = d/dx [f(x)]
f''(x) = d/dx [f'(x)]
Derivative of x^n = n*x^(n-1)

Theorems

Power Rule for Differentiation

Suitable Grade Level

Grades 11-12 (Advanced High School Calculus)