Chapter 7: Problem 25
Find the integrals Check your answers by differentiation. $$\int \sin \theta(\cos \theta+5)^{7} d \theta$$
Short Answer
Expert verified
The integral is \(-\frac{(\cos \theta + 5)^{8}}{8} + C\).
Step by step solution
01
Choose the Substitution
To find the integral \( \int \sin \theta(\cos \theta+5)^{7} \, d\theta \), let's use substitution. Since the integral involves \( \cos \theta + 5 \), set \( u = \cos \theta + 5 \).
02
Differentiate for Substitution
Differentiate \( u = \cos \theta + 5 \) with respect to \( \theta \): \( \frac{du}{d\theta} = -\sin \theta \), or \( du = -\sin \theta \, d\theta \). This can be rearranged to \( -du = \sin \theta \, d\theta \).
03
Substitute into the Integral
Replace \( \sin \theta \, d\theta \) in the integral with \( -du \), transforming the integral into: \( \int u^{7}(-du) \), which simplifies to \( -\int u^{7} \; du \).
04
Integrate
Integrate \( -\int u^{7} \; du \). The antiderivative of \( u^{7} \) is \( \frac{u^{8}}{8} \). Thus, \( -\int u^{7} \; du = -\frac{u^{8}}{8} + C \), where \( C \) is the constant of integration.
05
Reverse the Substitution
Return to the original variable by substituting back \( u = \cos \theta + 5 \): \( -\frac{(\cos \theta + 5)^{8}}{8} + C \).
06
Differentiate for Verification
Differentiate \( -\frac{(\cos \theta + 5)^{8}}{8} + C \) with respect to \( \theta \) to verify the result matches the original integrand. By the chain rule and simplifying, verify the derivative equals \( \sin \theta(\cos \theta+5)^{7} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Definite and Indefinite Integrals
In calculus, integrals are a way of adding up pieces to find the whole. There are two main types of integrals: definite and indefinite. Indefinite integrals, like the one in the given exercise, help us find families of functions whose derivative is the original function we started with. They come with a constant of integration, usually denoted by \( C \), because differentiation of a constant is zero and does not affect the original function.
Definite integrals, on the other hand, calculate the actual value between two points, giving a specific number as a result. Unlike indefinite integrals, there's no constant of integration because you're evaluating across a specific interval.
Definite integrals, on the other hand, calculate the actual value between two points, giving a specific number as a result. Unlike indefinite integrals, there's no constant of integration because you're evaluating across a specific interval.
- The integral symbol \( \int \) represents the integration process.
- In indefinite integrals, you're finding the antiderivative.
- For definite integrals, limits are placed on the integral sign to indicate the bounds.
Differentiation
Differentiation is essentially the reverse of integration and forms a foundation for solving calculus problems. It involves finding a derivative, which represents the rate of change of a function concerning its variable. In this exercise, you use differentiation for substitution and verification.
Let's look at how it's done: When you substitute \( u = \cos \theta + 5 \), you need to determine how \( u \) changes with respect to \( \theta \), hence, you differentiate. The result, \( \frac{du}{d\theta} = -\sin \theta \), simplifies the integral by allowing you to replace \( \sin \theta \, d\theta \) with \( -du \).
Let's look at how it's done: When you substitute \( u = \cos \theta + 5 \), you need to determine how \( u \) changes with respect to \( \theta \), hence, you differentiate. The result, \( \frac{du}{d\theta} = -\sin \theta \), simplifies the integral by allowing you to replace \( \sin \theta \, d\theta \) with \( -du \).
- Differentiation breaks down complex expressions into simpler parts.
- Verification using differentiation checks the correctness of your integral solution.
- It's a powerful tool for calculus problem solving, especially when verifying integrals.
Calculus Problem Solving
Solving calculus problems requires a strategic approach to untangle complexity. The problem-solving process often includes both integration and differentiation, as seen in this exercise. Here’s a step-by-step approach:1. **Recognize Patterns**: Identify whether substitution can simplify the function. Here, \( \cos \theta + 5 \) was pivotal.2. **Substitution**: Introduce a new variable \( u \) to the problem; a simpler form is easier to handle.3. **Differentiate for Substitution**: Determine \( \frac{du}{d\theta} \) to transform the integral.4. **Integration**: Once simpler, integrate the function. Always remember to account for constants of integration in indefinite integrals.5. **Reverse Substitution**: After integration, convert back to the original variable to provide final functions.6. **Verification via Differentiation**: Re-differentiate to ensure the integration was accurate.This logical sequence not only solves problems but also confirms your findings. It builds confidence and helps sharpen problem-solving skills. Success in calculus problem solving develops through practice and attention to these integrated methods.