Chapter 5: Problem 56
For each definite integral: a. Evaluate it "by hand." b. Check your answer by using a graphing calculator. $$ \int_{0}^{3} \sqrt{x^{2}+16} x d x $$
Short Answer
Expert verified
The value of the integral is approximately 20.33.
Step by step solution
01
Identify the Integral to Solve
We're given the integral: \( \int_{0}^{3} \sqrt{x^{2}+16} \cdot x \, dx \). Identify the integral as a definite integral with limits 0 and 3.
02
Simplification Using Substitution
Use substitution to simplify the integral. Let \( u = x^2 + 16 \), resulting in \( du = 2x \, dx \), or \( x \, dx = \frac{1}{2} du \). Then, change the limits of integration: when \( x = 0, u = 16 \); when \( x = 3, u = 25 \). The integral becomes \( \frac{1}{2} \int_{16}^{25} \sqrt{u} \, du \).
03
Evaluate the Integral
Evaluate the new integral \( \frac{1}{2} \int_{16}^{25} u^{1/2} \, du \). The antiderivative of \( u^{1/2} \) is \( \frac{2}{3}u^{3/2} \). So, the integral becomes \( \frac{1}{2} \left[ \frac{2}{3}u^{3/2} \right]_{16}^{25} = \frac{1}{3} [u^{3/2}]_{16}^{25} \).
04
Solve for Definite Integral Limits
Calculate \( \frac{1}{3} ([25^{3/2}] - [16^{3/2}]) \). \( 25^{3/2} = (25^{1/2})^3 = 5^3 = 125 \) and \( 16^{3/2} = (16^{1/2})^3 = 4^3 = 64 \). Substitute back into the equation \( \frac{1}{3} (125 - 64) = \frac{1}{3} \times 61 = 20.3333 \) (repeating).
05
Verification Using Graphing Calculator
Use a graphing calculator to verify the calculated value of the integral \( \int_{0}^{3} \sqrt{x^{2}+16} \cdot x \, dx \). Graphing calculators provide direct computation for double-checking the result found by hand.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Substitution Method in Integration
The substitution method is a handy technique used to simplify integrals. It especially comes into play when dealing with integrals that aren't straightforward to solve. The basic idea is to transform the original integral into a simpler one using a substitution.In the given problem, you notice the expression \( \sqrt{x^{2}+16} \cdot x \). Here, choosing a substitution can help in rewriting the function in a more digestible form. Let's dive into how it works:
- First, identify a part of the integrand that can be set equal to a new variable. In this case, letting \( u = x^2 + 16 \) simplifies the integral because the derivative of \( u \), \( du = 2x \, dx \), matches well with the remaining \( x \, dx \).
- Solving for \( x \, dx \) gives you \( x \, dx = \frac{1}{2} \, du \), which can substitute back into the integral.
- The limits of integration must change with respect to the new variable. So when \( x = 0 \), \( u = 16 \) and when \( x = 3 \), \( u = 25 \).
Antiderivatives
Antiderivatives play a crucial role in solving integrals. They are essentially the reverse process of differentiation; if you have a function, the antiderivative is a function whose derivative is the original function.For the problem at hand, once you've made the substitution, you are left to solve \( \frac{1}{2} \int_{16}^{25} u^{1/2} \, du \). The antiderivative of \( u^{1/2} \) is obtained as follows:
- The general rule for finding the antiderivative \( \int u^n \, du \) is \( \frac{u^{n+1}}{n+1} + C \) where \( C \) is a constant."
- Applying this rule, you get \( \frac{2}{3} u^{3/2} \) as the antiderivative of \( u^{1/2} \).
- \( 25^{3/2} = 125 \) and \( 16^{3/2} = 64 \).
- Finally, compute \( \frac{1}{3} (125 - 64) = 20.3333 \).
Graphical Verification of Integrals
Verifying the results of integration is vital to ensure accuracy. One of the most intuitive techniques is checking the solution using a graphing calculator. Graphical verification helps in comparing the analytical results you calculated by hand, with a numerically computed value.Here’s how this can be tackled in the context of our problem:
- After calculating the solution manually, input the integral into a graphing calculator: \( \int_{0}^{3} \sqrt{x^{2}+16} x \, dx \).
- The calculator will compute the definite integral and provide a result.
- Compare this graphed value with the manual answer, which was approximately 20.3333. A match confirms your solution’s accuracy.