Math Problem Statement

Integrate by parts

Integrate \( \sin^3(x) \, dx \)

Solution

The integral you've provided is:

sin3(x)dx\int \sin^3(x) \, dx

This integral can be solved using a combination of trigonometric identities and substitution rather than directly using integration by parts. However, let me guide you through it step by step.

Step 1: Rewrite sin3(x)\sin^3(x)

We can use the identity: sin3(x)=sin(x)sin2(x)\sin^3(x) = \sin(x) \cdot \sin^2(x) And recall that: sin2(x)=1cos2(x)\sin^2(x) = 1 - \cos^2(x) Thus: sin3(x)=sin(x)(1cos2(x))=sin(x)sin(x)cos2(x)\sin^3(x) = \sin(x) \cdot (1 - \cos^2(x)) = \sin(x) - \sin(x) \cos^2(x)

Step 2: Split the integral

Now, split the integral into two parts: sin3(x)dx=sin(x)dxsin(x)cos2(x)dx\int \sin^3(x) \, dx = \int \sin(x) \, dx - \int \sin(x) \cos^2(x) \, dx

Step 3: Solve the first integral

The first integral is straightforward: sin(x)dx=cos(x)\int \sin(x) \, dx = -\cos(x)

Step 4: Solve the second integral using substitution

For the second integral, use the substitution u=cos(x)u = \cos(x), which gives du=sin(x)dxdu = -\sin(x) \, dx. The integral becomes: sin(x)cos2(x)dx=u2du-\int \sin(x) \cos^2(x) \, dx = \int u^2 \, du The solution to this is: u2du=u33=cos3(x)3\int u^2 \, du = \frac{u^3}{3} = \frac{\cos^3(x)}{3}

Step 5: Combine results

Putting everything together, the solution is: sin3(x)dx=cos(x)+cos3(x)3+C\int \sin^3(x) \, dx = -\cos(x) + \frac{\cos^3(x)}{3} + C

This is the final result.

Do you want more details or have any questions?

Here are five related questions that could expand on this topic:

  1. How would you apply integration by parts to trigonometric functions?
  2. Can you generalize the method to integrate sinn(x)dx\sin^n(x) \, dx for other powers of nn?
  3. How would you solve the integral cos3(x)dx\int \cos^3(x) \, dx?
  4. What are the main differences between integration by substitution and by parts?
  5. How can we integrate other functions like sin(x)cos(x)\sin(x)\cos(x) using trigonometric identities?

Tip: Always check for trigonometric identities that can simplify the powers of sine or cosine before attempting direct integration.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Integration

Formulas

\( \sin^3(x) = \sin(x)(1 - \cos^2(x)) \)
Trigonometric identities

Theorems

Substitution method in integration

Suitable Grade Level

Grades 11-12, University level