Chapter 5: Problem 60
For each definite integral: a. Evaluate it "by hand." b. Check your answer by using a graphing calculator. $$ \int_{1}^{4} \frac{e^{\sqrt{x}}}{\sqrt{x}} d x $$
Short Answer
Expert verified
The integral evaluates to \( 2(e^2 - e) \).
Step by step solution
01
Understanding the Integral
We need to evaluate the integral \( \int_{1}^{4} \frac{e^{\sqrt{x}}}{\sqrt{x}} \, dx \). This integral can be solved using substitution.
02
Setting up Substitution
Let \( u = \sqrt{x} \) which implies that \( x = u^2 \). Then, the differential \( dx = 2u \, du \). Substituting these into the integral, we change the limits of integration as well. When \( x = 1 \), \( u = 1 \), and when \( x = 4 \), \( u = 2 \).
03
Substitute and Simplify
Substitute the values from Step 2 into the integral:\[ \int_{1}^{2} \frac{e^u}{u} \, (2u \, du) = 2 \int_{1}^{2} e^u \, du \] This simplifies to \( 2 \int_{1}^{2} e^u \, du \).
04
Evaluate the Integral
The integral \( \int_{1}^{2} e^u \, du \) is straightforward:\[ \int_{1}^{2} e^u \, du = \left[ e^u \right]_{1}^{2} = e^2 - e^1 \] Thus, \( 2 \int_{1}^{2} e^u \, du = 2(e^2 - e^1) = 2(e^2 - e) \).
05
Verification with Graphing Calculator
Using a graphing calculator, input \( \int_{1}^{4} \frac{e^{\sqrt{x}}}{\sqrt{x}} \, dx \). Ensure that the calculator settings are correct and ensure the computed area under the curve matches \( 2(e^2 - e) \). If they match, the solution is verified.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Substitution Method
The substitution method is a powerful tool in solving integrals, especially when the function seems complicated. In this exercise, we solve the integral \( \int_{1}^{4} \frac{e^{\sqrt{x}}}{\sqrt{x}} \, dx \) using substitution, a common integration technique. Here’s a simplified way:
- We look for a substitution that will simplify the integral. Here, we choose \( u = \sqrt{x} \), which transforms our integral into one that's easier to manage.
- Once we set \( u = \sqrt{x} \), \( x \) becomes \( u^2 \), and the differential \( dx \) is replaced with \( 2u \, du \).
- Substitution often requires adjusting the limits of integration. With \( x = 1 \), \( u = 1 \), and when \( x = 4 \), \( u = 2 \).
Integration Techniques
A variety of integration techniques exist to evaluate integrals like the one in this problem. After substitution, we arrive at the integral \( 2 \int_{1}^{2} e^u \, du \). This integral is direct because the antiderivative of \( e^u \) is simply \( e^u \):
- Evaluate \( \int e^u \, du \) to get \( e^u \).
- Apply the fundamental theorem of calculus by substituting the limits of integration back into the equation: \[ e^u \bigg|_{1}^{2} = e^2 - e^1. \]
- Finally, multiply the result by 2 to account for the substitution factor, leading to \( 2(e^2 - e) \).
Graphing Calculator Verification
Verification of manual calculations using technology is a standard practice, especially in calculus. A graphing calculator can be a valuable tool for verifying your solutions in definite integrals. By inputting the original integral \( \int_{1}^{4} \frac{e^{\sqrt{x}}}{\sqrt{x}} \, dx \) into the calculator, students can:
- Ensure they set the calculator with the correct integral expression and limits for accurate results.
- Observe the computed area under the curve, offering a visual understanding of the integral.
- Compare the calculator’s result with their manually derived solution, which in this instance should show \( 2(e^2 - e) \).