Math Problem Statement

solve

If ∫ |x - 4| dx from -b to b = 47, find the value of b^2.

Solution

It seems there was an issue solving the equation directly for bb. Let's solve the problem step-by-step.

We need to solve the integral: bbx4dx=47\int_{-b}^{b} |x - 4| \, dx = 47

Step-by-Step Solution

  1. Understanding the Absolute Value Function: The function x4|x - 4| has a critical point at x=4x = 4. This divides the integral into two parts:

    \begin{cases} 4 - x & \text{if } x < 4 \\ x - 4 & \text{if } x \geq 4 \end{cases}$$
  2. Case Analysis for the Integral:

    • If b4b \leq 4: bbx4dx=bb(4x)dx\int_{-b}^{b} |x - 4| \, dx = \int_{-b}^{b} (4 - x) \, dx This case doesn't match the given integral result since the integral value is quite large (47), suggesting bb is greater than 4.

    • If b>4b > 4: bbx4dx=b4(4x)dx+4b(x4)dx\int_{-b}^{b} |x - 4| \, dx = \int_{-b}^{4} (4 - x) \, dx + \int_{4}^{b} (x - 4) \, dx

  3. Evaluating the Integral:

    • For b4(4x)dx\int_{-b}^{4} (4 - x) \, dx: b4(4x)dx=[4xx22]b4\int_{-b}^{4} (4 - x) \, dx = \left[ 4x - \frac{x^2}{2} \right]_{-b}^{4} =(44422)(4(b)(b)22)= \left( 4 \cdot 4 - \frac{4^2}{2} \right) - \left( 4(-b) - \frac{(-b)^2}{2} \right) =(168)(4bb22)= (16 - 8) - (-4b - \frac{b^2}{2}) =8+4b+b22= 8 + 4b + \frac{b^2}{2}

    • For 4b(x4)dx\int_{4}^{b} (x - 4) \, dx: 4b(x4)dx=[x224x]4b\int_{4}^{b} (x - 4) \, dx = \left[ \frac{x^2}{2} - 4x \right]_{4}^{b} =(b224b)(42244)= \left( \frac{b^2}{2} - 4b \right) - \left( \frac{4^2}{2} - 4 \cdot 4 \right) =b224b(816)= \frac{b^2}{2} - 4b - (8 - 16) =b224b+8= \frac{b^2}{2} - 4b + 8

  4. Combining Both Parts: bbx4dx=(8+4b+b22)+(b224b+8)\int_{-b}^{b} |x - 4| \, dx = \left( 8 + 4b + \frac{b^2}{2} \right) + \left( \frac{b^2}{2} - 4b + 8 \right) =8+8+4b4b+b22+b22= 8 + 8 + 4b - 4b + \frac{b^2}{2} + \frac{b^2}{2} =16+b2= 16 + b^2

  5. Setting Up the Equation: 16+b2=4716 + b^2 = 47

  6. Solving for b2b^2: b2=4716b^2 = 47 - 16 b2=31b^2 = 31

Therefore, the value of b2b^2 is 3131.

Do you want more details or have any questions?

Here are 5 related questions for further exploration:

  1. How do you integrate absolute value functions in general?
  2. What are the properties of definite integrals involving absolute value functions?
  3. Can you explain the geometric interpretation of the integral of x4|x - 4|?
  4. How would the solution change if the limits of integration were different?
  5. What if the integrand was xc|x - c| for some constant cc? How would you approach the problem?

Tip: When dealing with absolute value integrals, always identify the points where the expression inside the absolute value changes sign. This helps in splitting the integral into manageable parts.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Absolute Value Functions
Definite Integrals

Formulas

∫ |x - c| dx = Piecewise function based on x compared to c

Theorems

Fundamental Theorem of Calculus
Properties of Definite Integrals

Suitable Grade Level

Grade 11-12 or early university calculus