Math Problem Statement

integral of the absolute value of sinx

Solution

The integral of the absolute value of sin(x)\sin(x), denoted by sin(x)dx\int |\sin(x)| \, dx, can be approached by breaking the function into intervals where sin(x)\sin(x) is positive or negative. This is because the absolute value function affects the behavior of sin(x)\sin(x) differently depending on the interval.

Step-by-Step Solution

  1. Break the integral into intervals:

    sin(x)\sin(x) is positive on the interval [2nπ,(2n+1)π][2n\pi, (2n+1)\pi], and negative on the interval [(2n+1)π,(2n+2)π][(2n+1)\pi, (2n+2)\pi] for integer nn. Thus, the absolute value of sin(x)\sin(x) can be handled by splitting the integral into two parts.

  2. Positive intervals (where sin(x)0\sin(x) \geq 0): On [2nπ,(2n+1)π][2n\pi, (2n+1)\pi], sin(x)=sin(x)|\sin(x)| = \sin(x). The integral in this region is: sin(x)dx=cos(x)+C\int \sin(x) \, dx = -\cos(x) + C

  3. Negative intervals (where sin(x)<0\sin(x) < 0): On [(2n+1)π,(2n+2)π][(2n+1)\pi, (2n+2)\pi], sin(x)=sin(x)|\sin(x)| = -\sin(x). The integral in this region is: sin(x)dx=cos(x)+C\int -\sin(x) \, dx = \cos(x) + C

  4. General formula: The integral of sin(x)|\sin(x)| over a full period, from 00 to 2π2\pi, is the sum of the integrals over the intervals [0,π][0, \pi] and [π,2π][\pi, 2\pi]: 0πsin(x)dx+π2πsin(x)dx\int_0^\pi \sin(x) \, dx + \int_\pi^{2\pi} -\sin(x) \, dx

    Evaluating these: 0πsin(x)dx=[cos(x)]0π=2\int_0^\pi \sin(x) \, dx = [-\cos(x)]_0^\pi = 2 π2πsin(x)dx=[cos(x)]π2π=2\int_\pi^{2\pi} -\sin(x) \, dx = [\cos(x)]_\pi^{2\pi} = 2

    Therefore, over a full period: 02πsin(x)dx=2+2=4\int_0^{2\pi} |\sin(x)| \, dx = 2 + 2 = 4

Final Answer:

The indefinite integral of sin(x)|\sin(x)| is a piecewise function, depending on the intervals where sin(x)\sin(x) is positive or negative. Over one period [0,2π][0, 2\pi], the integral evaluates to 44.

Would you like more details on any step or further clarifications?

Here are some related questions:

  1. What is the integral of cos(x)\cos(x)?
  2. How can you calculate the area under the curve of sin(x)\sin(x)?
  3. How do you handle integrals involving absolute values of more complex functions?
  4. How does the integral of sin(x)\sin(x) change over different intervals?
  5. What is the Fourier series of sin(x)|\sin(x)|?

Tip: Always check the periodicity of trigonometric functions when solving integrals, as they can help simplify the calculations.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Integral Calculus
Trigonometric Functions
Absolute Value

Formulas

∫ |sin(x)| dx
∫ sin(x) dx = -cos(x) + C
∫ -sin(x) dx = cos(x) + C

Theorems

Periodic nature of trigonometric functions
Piecewise integration for absolute value functions

Suitable Grade Level

Grades 11-12, College Level Calculus