Chapter 31: Problem 13
Evaluate \(\int_{1}^{4}\left(\frac{\theta+2}{\sqrt{\theta}}\right) \mathrm{d} \theta\), taking positive square roots only.
Short Answer
Expert verified
The value of the integral is \( \frac{20}{3} \).
Step by step solution
01
Simplify the Integrand
We start by simplifying the given integrand. The function to integrate is \( \frac{\theta + 2}{\sqrt{\theta}} \). We can split this into two separate terms: \( \frac{\theta}{\sqrt{\theta}} + \frac{2}{\sqrt{\theta}} \). Simplifying each term gives \( \theta^{1/2} + 2\theta^{-1/2} \).
02
Set Up the Integral
With the expression simplified, set up the integral for each term separately: \[ \int_{1}^{4} \theta^{1/2} \,d\theta + 2 \int_{1}^{4} \theta^{-1/2} \,d\theta \]
03
Integrate Each Term
Integrate each term using the power rule for integrals:- For \( \int \theta^{1/2} \,d\theta \), the result is \( \frac{2}{3} \theta^{3/2} \).- For \( \int \theta^{-1/2} \,d\theta \), the result is \( 2\theta^{1/2} \).
04
Substitute Boundaries and Evaluate
For each integrated term, substitute the upper and lower bounds of the integral (4 and 1) and evaluate:- For \( \frac{2}{3} \theta^{3/2} \) from 1 to 4, compute: \( \frac{2}{3} \times 4^{3/2} - \frac{2}{3} \times 1^{3/2} = \frac{2}{3} \times 8 - \frac{2}{3} \times 1 = \frac{16}{3} - \frac{2}{3} = \frac{14}{3} \).- For \( 2\theta^{1/2} \) from 1 to 4, compute: \( 2 \times 4^{1/2} - 2 \times 1^{1/2} = 2 \times 2 - 2 = 4 - 2 = 2 \).
05
Sum the Results
Sum the results from each evaluated integration:\[ \frac{14}{3} + 2 = \frac{14}{3} + \frac{6}{3} = \frac{20}{3} \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integrand Simplification
Integrand simplification is a core step in making complex integrals easier to solve. In this exercise, the integrand given is \( \frac{\theta + 2}{\sqrt{\theta}} \), which at first glance, looks a bit tricky. However, by breaking it down, the expression becomes much simpler to handle. To simplify, divide the numerator terms individually by the denominator. This results in:
- \( \frac{\theta}{\sqrt{\theta}} \) which simplifies to \( \theta^{1/2} \).
- \( \frac{2}{\sqrt{\theta}} \) which simplifies to \( 2\theta^{-1/2} \).
Power Rule for Integration
The power rule for integration is a fundamental tool in calculus. It simplifies the process of finding the integral of functions that are powers of a variable. The general power rule for integration states: Given a function \( f(x) = x^n \), the integral is \( \int x^n \,dx = \frac{1}{n+1} x^{n+1} + C \), where \( n eq -1 \).Applying this rule, we can integrate each part of the simplified integrand:
- For \( \theta^{1/2} \), the integral \( \int \theta^{1/2} \,d\theta \) becomes \( \frac{2}{3} \theta^{3/2} \).
- For \( 2\theta^{-1/2} \), the integral \( 2 \int \theta^{-1/2} \,d\theta \) becomes \( 2 \times 2\theta^{1/2} = 4\theta^{1/2} \).
Evaluating Definite Integrals
Evaluating a definite integral means finding the net area under a curve between two specified bounds. This involves substituting the limits into the integrated function and calculating their difference.For our problem, the limits are 1 and 4. We proceed as follows:
- For \( \frac{2}{3} \theta^{3/2} \), substitute \( \theta = 4 \) and \( \theta = 1 \) to calculate \( \left( \frac{2}{3} \times 4^{3/2} \right) - \left( \frac{2}{3} \times 1^{3/2} \right) = \frac{14}{3} \).
- For \( 4\theta^{1/2} \), substitute to find \( \left( 4 \times 4^{1/2} \right) - \left( 4 \times 1^{1/2} \right) = 2 \).