Math Problem Statement

Find the integrals ∫[-5 to 5] f(x)dx and ∫[-5 to 5] |f(x)|dx, where f(x) is a continuous, non-negative function on [0, 5], with ∫[0 to 5] f(x)dx = 10. Solve for the cases where (i) f is an even function, and (ii) f is an odd function.

Solution

Let's solve the questions step by step based on the problem provided:


Given Information:

  • 05f(x)dx=10\int_0^5 f(x) \, dx = 10
  • f(x)f(x) is continuous and non-negative on [0,5][0, 5].

You are tasked to find:

  1. 55f(x)dx\int_{-5}^5 f(x) \, dx
  2. 55f(x)dx\int_{-5}^5 |f(x)| \, dx

Under the following conditions:

  1. f(x)f(x) is an even function.
  2. f(x)f(x) is an odd function.

1. If f(x)f(x) is an even function:

For even functions, f(x)=f(x)f(-x) = f(x).

  1. Finding 55f(x)dx\int_{-5}^5 f(x) \, dx:

    • Due to symmetry: 55f(x)dx=205f(x)dx.\int_{-5}^5 f(x) \, dx = 2 \int_0^5 f(x) \, dx.
    • Substituting the given value: 55f(x)dx=210=20.\int_{-5}^5 f(x) \, dx = 2 \cdot 10 = 20.
  2. Finding 55f(x)dx\int_{-5}^5 |f(x)| \, dx:

    • Since f(x)0f(x) \geq 0 (non-negative), f(x)=f(x)|f(x)| = f(x). 55f(x)dx=55f(x)dx.\int_{-5}^5 |f(x)| \, dx = \int_{-5}^5 f(x) \, dx.
    • Thus: 55f(x)dx=20.\int_{-5}^5 |f(x)| \, dx = 20.

2. If f(x)f(x) is an odd function:

For odd functions, f(x)=f(x)f(-x) = -f(x).

  1. Finding 55f(x)dx\int_{-5}^5 f(x) \, dx:

    • Due to symmetry, the integral of an odd function over symmetric limits is 0: 55f(x)dx=0.\int_{-5}^5 f(x) \, dx = 0.
  2. Finding 55f(x)dx\int_{-5}^5 |f(x)| \, dx:

    • The absolute value of f(x)f(x) (an odd function) makes it an even function: f(x)=f(x) for x<0andf(x)=f(x) for x0.|f(x)| = -f(x) \text{ for } x < 0 \quad \text{and} \quad |f(x)| = f(x) \text{ for } x \geq 0.
    • Thus: 55f(x)dx=205f(x)dx.\int_{-5}^5 |f(x)| \, dx = 2 \int_0^5 f(x) \, dx.
    • Substituting the given value: 55f(x)dx=210=20.\int_{-5}^5 |f(x)| \, dx = 2 \cdot 10 = 20.

Final Answers:

  1. When f(x)f(x) is even:

    • 55f(x)dx=20\int_{-5}^5 f(x) \, dx = 20
    • 55f(x)dx=20\int_{-5}^5 |f(x)| \, dx = 20
  2. When f(x)f(x) is odd:

    • 55f(x)dx=0\int_{-5}^5 f(x) \, dx = 0
    • 55f(x)dx=20\int_{-5}^5 |f(x)| \, dx = 20

Do you need any clarifications or further breakdowns?

Here are some related questions:

  1. How do odd and even functions affect integrals over symmetric intervals?
  2. Why does the absolute value affect odd functions but not even functions?
  3. Can we compute abf(x)dx\int_{a}^b |f(x)| \, dx directly without symmetry arguments?
  4. What happens if f(x)f(x) is neither odd nor even?
  5. How does the non-negativity of f(x)f(x) simplify this problem?

Tip: Always use symmetry properties of functions to simplify definite integrals over symmetric intervals.

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Math Problem Analysis

Mathematical Concepts

Properties of definite integrals
Even and odd functions
Absolute value of functions

Formulas

For even functions: ∫[-a to a] f(x)dx = 2∫[0 to a] f(x)dx
For odd functions: ∫[-a to a] f(x)dx = 0
Absolute value: |f(x)| ensures non-negativity

Theorems

Symmetry of even and odd functions
Properties of absolute value in integration

Suitable Grade Level

Undergraduate Mathematics