Chapter 5: Problem 24
Evaluate the integrals in Exercises \(1-28\). $$\int_{1}^{8} \frac{\left(x^{1 / 3}+1\right)\left(2-x^{2 / 3}\right)}{x^{1 / 3}} d x$$
Short Answer
Expert verified
The integral evaluates to 2.4.
Step by step solution
01
Expand the integrand
We begin by expanding the integrand. Multiply the expressions in the numerator:\[ (x^{1/3} + 1)(2 - x^{2/3}) = 2x^{1/3} + 2 - x^{2/3}x^{1/3} - x^{2/3}. \]This expands to:\[ 2x^{1/3} + 2 - x - x^{2/3}. \]
02
Simplify the fraction
The integrand is:\[ \frac{2x^{1/3} + 2 - x - x^{2/3}}{x^{1/3}}. \]Simplify by dividing each term in the numerator by \(x^{1/3}\):\[ \frac{2x^{1/3}}{x^{1/3}} + \frac{2}{x^{1/3}} - \frac{x}{x^{1/3}} - \frac{x^{2/3}}{x^{1/3}} = 2 + 2x^{-1/3} - x^{2/3} - x^{1/3}. \]
03
Integrate term by term
Each term can now be integrated separately. We integrate:1. \( \int 2 \, dx = 2x + C_1 \)2. \( \int 2x^{-1/3} \, dx = 3x^{2/3} + C_2 \)3. \( \int -x^{2/3} \, dx = -\frac{3}{5}x^{5/3} + C_3 \)4. \( \int -x^{1/3} \, dx = -\frac{3}{4}x^{4/3} + C_4 \)
04
Evaluate the definite integral
Combine the results from Step 3 to form the indefinite integral:\[ \int \left(2 + 2x^{-1/3} - x^{2/3} - x^{1/3}\right) dx = 2x + 3x^{2/3} - \frac{3}{5}x^{5/3} - \frac{3}{4}x^{4/3} + C. \]Evaluate from \(x = 1\) to \(x = 8\):\[ \left[ 2x + 3x^{2/3} - \frac{3}{5}x^{5/3} - \frac{3}{4}x^{4/3} \right]_1^8. \]
05
Substitute the bounds and compute
Substitute the bounds into the calculated expression:- At \(x=8\):\[ 2(8) + 3(8^{2/3}) - \frac{3}{5}(8^{5/3}) - \frac{3}{4}(8^{4/3}). \] Simplify to get specific numeric values. Compute using the fact that: - \(8^{1/3} = 2\), so \(8^{2/3} = 4\) and \(8^{5/3} = 32\), and \(8^{4/3} = 16\).- At \(x=1\):\[ 2(1) + 3(1) - \frac{3}{5}(1) - \frac{3}{4}(1). \]Subtract the evaluated results for \(x=1\) from those at \(x=8\).
06
Final calculation and result
Complete the subtraction from Step 5:\[ \left(16 + 3(4) - \frac{3}{5}(32) - \frac{3}{4}(16)\right) - \left(2 + 3 - \frac{3}{5} - \frac{3}{4}\right). \]Now simplify both expressions, calculate all terms and finalize: \( = 2.4 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration Techniques
Integration is like finding the area under a curve. When we talk about definite integrals, we're focusing on a specific interval on the curve between two points.
In this problem, we're using basic integration techniques to solve it efficiently. Here's a quick rundown:
In this problem, we're using basic integration techniques to solve it efficiently. Here's a quick rundown:
- Breakdown: Once you have a function, it's usually helpful to break it down term by term. This makes integration easier.
- Indefinite to Definite: Begin with solving the indefinite integral, then apply the limits of integration to evaluate the definite integral.
- Linearity: Integration can be done separately on each term of a polynomial. This helps to keep things simple and manageable.
Exponent Rules
When dealing with functions that include exponents, it’s essential to use exponent rules correctly.
Here's a simple guide to handling these scenarios:
Here's a simple guide to handling these scenarios:
- Dividing Exponents: When dividing like bases, subtract the exponents: \(x^a / x^b = x^{a-b}\).
- Power of a Power: This rule helps when you have powers raised to powers: \((x^m)^n = x^{m*n}\).
- Negative Exponents: Remember, \(x^{-a} = 1/x^a\).
- Roots as Exponents: A cube root of \(x\) is expressed as \(x^{1/3}\).
Polynomial Expansion
Expanding a polynomial involves multiplying expressions within parentheses. Let's break it down this way:
- Combine and Distribute: Distribute each term in one polynomial across the terms in the other; for example, distribute \( (x^{1/3} + 1) \) across \( (2 - x^{2/3}) \).
- Combine Like Terms: After distribution, combine like terms to simplify the expression. For instance, \(2x^{1/3} \) is the result of multiplying inside the polynomial.
Numerical Evaluation
Once you've performed the integration of each term and obtained a solid expression, you need to evaluate it numerically over the given limits.
Let's simplify this process:
Let's simplify this process:
- Plug Limits into Indefinite Integral: First, substitute the upper limit (\(x = 8\)) into the integrated expression, and then the lower limit (\(x = 1\)).
- Subtract: Subtract the value obtained at the lower limit from that obtained at the upper limit to get the definite integral's value.
- Calculate Powers: It's crucial to compute powers correctly based on previously mentioned rules—this ensures precise results.