Math Problem Statement

Evaluate the integral ∫ sin^4(x) cos^3(x) dx.

Solution

This integral can be solved using trigonometric identities and substitution techniques. Let’s solve it step-by-step:

We aim to evaluate:

sin4xcos3xdx\int \sin^4 x \cos^3 x \, dx

Step 1: Break the powers and use substitution

To simplify, we split cos3x\cos^3 x as: cos3x=cos2xcosx=(1sin2x)cosx\cos^3 x = \cos^2 x \cdot \cos x = (1 - \sin^2 x)\cos x

So the integral becomes: sin4xcos3xdx=sin4x(1sin2x)cosxdx\int \sin^4 x \cos^3 x \, dx = \int \sin^4 x (1 - \sin^2 x) \cos x \, dx

Step 2: Substitution

Let u=sinxu = \sin x, which gives du=cosxdxdu = \cos x \, dx. The limits and powers of sin\sin will update accordingly. Substituting, the integral becomes: sin4x(1sin2x)cosxdx=u4(1u2)du\int \sin^4 x (1 - \sin^2 x) \cos x \, dx = \int u^4 (1 - u^2) \, du

Step 3: Expand and simplify

Expand u4(1u2)u^4(1 - u^2): u4(1u2)=u4u6u^4(1 - u^2) = u^4 - u^6

So the integral becomes: u4u6du\int u^4 - u^6 \, du

Step 4: Integrate term by term

u4du=u55,u6du=u77\int u^4 \, du = \frac{u^5}{5}, \quad \int u^6 \, du = \frac{u^7}{7}

Thus: u4u6du=u55u77+C\int u^4 - u^6 \, du = \frac{u^5}{5} - \frac{u^7}{7} + C

Step 5: Substitute back u=sinxu = \sin x

Finally, substituting u=sinxu = \sin x back into the result gives: sin5x5sin7x7+C\frac{\sin^5 x}{5} - \frac{\sin^7 x}{7} + C

Final Answer:

sin5x5sin7x7+C\boxed{\frac{\sin^5 x}{5} - \frac{\sin^7 x}{7} + C}

Would you like further clarification or details?

Here are some related questions for you to consider:

  1. How do you decide when substitution is the best method for solving integrals?
  2. Can you apply a similar method to solve sin5xcos3xdx\int \sin^5 x \cos^3 x \, dx?
  3. What are the steps for integrating powers of trigonometric functions like sinnx\sin^n x and cosmx\cos^m x?
  4. How does the Pythagorean identity simplify trigonometric integrals?
  5. How can integration by parts apply to trigonometric integrals?

Tip: When solving integrals involving even or odd powers of sinx\sin x or cosx\cos x, consider substitution or using trigonometric identities strategically!

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Math Problem Analysis

Mathematical Concepts

Integration of Trigonometric Functions
Substitution Method
Expansion of Powers
Trigonometric Identities

Formulas

cos^2(x) = 1 - sin^2(x)
Substitution u = sin(x), du = cos(x) dx
∫ u^n du = u^(n+1)/(n+1) + C

Theorems

Trigonometric Pythagorean Identity
Power Rule for Integration

Suitable Grade Level

Undergraduate Calculus or Advanced High School Calculus