Chapter 5: Problem 50
Find \(\int_{0}^{5} f(x) d x\) if $$ f(x)=\left\\{\begin{array}{ll}{3} & {\text { for } x<3} \\ {x} & {\text { for } x \geqslant 3}\end{array}\right. $$
Short Answer
Expert verified
The value of the integral is 17.
Step by step solution
01
Understand the Piecewise Function
The function \( f(x) \) is defined as a piecewise function. For values of \( x \) from 0 to less than 3, \( f(x) = 3 \). For values of \( x \) greater than or equal to 3, \( f(x) = x \).
02
Split the Integral
Since the function is defined piecewise, split the integral at the point where the definition of the function changes, from 0 to 3 and from 3 to 5. The integral can be written as: \[ \int_{0}^{5} f(x) \, dx = \int_{0}^{3} 3 \, dx + \int_{3}^{5} x \, dx. \]
03
Integrate the First Interval
Calculate the integral of the constant function over the first interval: \[ \int_{0}^{3} 3 \, dx = 3 \times (3 - 0) = 9. \]
04
Integrate the Second Interval
Calculate the integral over the second interval: \[ \int_{3}^{5} x \, dx = \left[ \frac{x^2}{2} \right]_{3}^{5}. \] Evaluate the integral: \[ \frac{5^2}{2} - \frac{3^2}{2} = \frac{25}{2} - \frac{9}{2} = \frac{16}{2} = 8. \]
05
Sum the Results
Add the results of the two integrals from Step 3 and Step 4: \[ 9 + 8 = 17. \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Piecewise Functions
A piecewise function is a function composed of different expressions over different intervals. These are primarily useful when a function has distinct behaviors over its domain. In our problem, the piecewise function is defined as follows:
- For values of \( x \) less than 3, \( f(x) = 3 \). This means from 0 to less than 3, the function is a constant horizontal line at \( y = 3 \).
- For values of \( x \) that are 3 or greater, \( f(x) = x \). Here, the function is simply the line \( y = x \).
The Concept of Definite Integrals
Definite integrals are an important concept in calculus, allowing us to find the net area under a curve from one point to another along the x-axis. Unlike indefinite integrals, which include a constant of integration, definite integrals yield a numeric result that represents the total accumulated value over a specified interval.When working with a piecewise function, as seen in our exercise, the definite integral must be split into separate integrals over each defined segment:
- From 0 to 3 for the constant function \( f(x) = 3 \).
- From 3 to 5 for the linear function \( f(x) = x \).
Basics of Calculus and Integration
Calculus is a branch of mathematics that deals with change and motion, utilizing concepts such as derivatives and integrals. One of the core purposes of calculus is to understand how things accumulate; integration specifically helps calculate the total value of a function over an interval.In our exercise, integration is used to accumulate the total value of the piecewise function over its domain. Here, integration encompasses:
- Calculating the area under the constant segment of the function, which results in simply multiplying the value by the width of the interval.
- Applying the power rule for integration to determine the accumulated value of the linear segment \( f(x) = x \).