Math Problem Statement

Find the particular solution of the differential equation that satisfies the initial equations. f''(x) = -4 / (x-1)^2 - 2, f'(2) = 0, f(2) = 5, x > 1

Solution

To solve this problem, let's follow these steps systematically:

  1. Integrate f(x)f''(x) to find f(x)f'(x): f(x)=4(x1)22f''(x) = -\frac{4}{(x-1)^2} - 2 Integrate f(x)f''(x) with respect to xx.

  2. Integrate f(x)f'(x) to find f(x)f(x): After obtaining f(x)f'(x), integrate again to find f(x)f(x).

  3. Apply the initial conditions: Use f(2)=0f'(2) = 0 and f(2)=5f(2) = 5 to determine the constants of integration.


Step 1: Integrating f(x)f''(x)

We start with: f(x)=4(x1)22f''(x) = -\frac{4}{(x-1)^2} - 2 The integral of 4(x1)2-\frac{4}{(x-1)^2} is: 4(x1)2dx=4x1\int -\frac{4}{(x-1)^2} dx = \frac{4}{x-1} The integral of 2-2 is: 2dx=2x\int -2 \, dx = -2x Thus: f(x)=4x12x+C1f'(x) = \frac{4}{x-1} - 2x + C_1


Step 2: Integrating f(x)f'(x)

Now integrate f(x)f'(x): f(x)=4x12x+C1f'(x) = \frac{4}{x-1} - 2x + C_1 The integral of 4x1\frac{4}{x-1} is: 4x1dx=4lnx1\int \frac{4}{x-1} dx = 4 \ln|x-1| The integral of 2x-2x is: 2xdx=x2\int -2x \, dx = -x^2 The integral of C1C_1 is: C1dx=C1x\int C_1 \, dx = C_1x Thus: f(x)=4lnx1x2+C1x+C2f(x) = 4 \ln|x-1| - x^2 + C_1x + C_2


Step 3: Applying Initial Conditions

Using f(2)=0f'(2) = 0: f(x)=4x12x+C1f'(x) = \frac{4}{x-1} - 2x + C_1 Substitute x=2x = 2: 0=4212(2)+C10 = \frac{4}{2-1} - 2(2) + C_1 0=44+C1    C1=00 = 4 - 4 + C_1 \quad \implies \quad C_1 = 0

Using f(2)=5f(2) = 5: f(x)=4lnx1x2+C1x+C2f(x) = 4 \ln|x-1| - x^2 + C_1x + C_2 Substitute x=2x = 2 and C1=0C_1 = 0: 5=4ln2122+C25 = 4 \ln|2-1| - 2^2 + C_2 5=4ln(1)4+C25 = 4 \ln(1) - 4 + C_2 5=04+C2    C2=95 = 0 - 4 + C_2 \quad \implies \quad C_2 = 9


Final Solution

Substitute C1=0C_1 = 0 and C2=9C_2 = 9 into f(x)f(x): f(x)=4lnx1x2+9f(x) = 4 \ln|x-1| - x^2 + 9

For x>1x > 1, lnx1=ln(x1)\ln|x-1| = \ln(x-1). Therefore: f(x)=4ln(x1)x2+9f(x) = 4 \ln(x-1) - x^2 + 9


Let me know if you want further details or have any questions! Here are some related questions to consider:

  1. How is the constant of integration determined in differential equations?
  2. Why is lnx1\ln|x-1| used when integrating 1x1\frac{1}{x-1}?
  3. How can you confirm that this solution satisfies the original differential equation?
  4. What happens if the initial conditions are different?
  5. How does x>1x > 1 simplify lnx1\ln|x-1| to ln(x1)\ln(x-1)?

Tip: Always verify the solution by substituting it back into the original differential equation!

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Integration
Initial Value Problems
Natural Logarithm

Formulas

∫ (-4 / (x-1)^2) dx = 4 / (x-1)
∫ -2 dx = -2x
f'(x) = 4 / (x-1) - 2x + C1
f(x) = 4 ln|x-1| - x^2 + C1x + C2

Theorems

Fundamental Theorem of Calculus
Properties of Integrals
Initial Value Problem Solution

Suitable Grade Level

Undergraduate Calculus