Concepts and Vocabulary
True or False \(\int_{2}^{3} (x^{2}+x)\, dx=\int_{2}^{3} x^{2}dx+\int_{2}^{3} x\, dx\)
True or False \(\int_{0}^{3}5e^{x^{2}}dx=\int_{0}^{3}5\, dx\cdot \int_{0}^{3}e^{x^{2}}dx\)
True or False \(\int_{0}^{5} (x^{3}+1) dx=\int_{0}^{-3}( x^{3}+1)dx\) \(+\int_{-3}^{5} (x^{3}+1) dx\)
If \(f\) is continuous on an interval containing the numbers \(a,\) \(b\), and \(c,\) and if \(\int_{a}^{c}f(x)\, dx=3\) and \(\int_{c}^{b}f(x)\, dx=-5,\) then \(\int_{a}^{b}f(x) dx=\)_________.
If a function \(f\) is continuous on the closed interval \([a,b],\) then \(\bar{y}=\dfrac{1}{b-a}\int_{a}^{b}f(x)\,dx\) is the ______ ______ of \(f\) over \([a,b].\)
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True or False If a function \(f\) is continuous on a closed interval \([a,b]\) and if \(m\) and \(M\) denote the absolute minimum value and the absolute maximum value, respectively, of \(f\) on \([a,b]\), then \[ m\leq \int_{a}^{b}f(x)\,dx\leq M. \]
Skill Building
In Problems 7–12, find each definite integral given that \({\int_{1}^{3}{f(x)\,dx}}=5\), \({\int_{1}^{3}}\,g{(x)\,dx}={-}2\), \({\int_{3}^{5}{f(x)\,dx}}=2\), \({\int_{3}^{5}{g(x)\,dx}}=1.\)
\(\int_{1}^{3} [f(x)-g(x)]\,dx \)
\(\int_{1}^{3} [f(x)+g(x)]\,dx \)
\(\int_{1}^{3} [5f(x)-3g(x)]\,dx \)
\(\int_{1}^{3}[3f(x)+4g(x)]\,dx\)
\(\int_{1}^{5}[2f(x)-3g(x)]\,dx \)
\(\int_{1}^{5}[f(x)-g(x)]\,dx\)
In Problems 13–32, find each definite integral using the Fundamental Theorem of Calculus.
\(\int_{0}^{1}{({t^{2}-t^{3/2}})}\,dt \)
\(\int_{-2}^{0}{({x+x^{2}})\, dx}\)
\(\int_{\pi /2}^{\pi}{4\sin x\, dx}\)
\(\int_{0}^{1}{3x^{2}} dx \)
\(\int_{1}^{e}-\dfrac{3}{x}\,dx\)
\(\int_{e}^{8}\dfrac{1}{2x}dx\)
\(\int_{-\pi /4}^{\pi /4}(1+2\sec x\,\tan x)\,dx \)
\(\int_{0}^{\pi /4}(1+\sec ^{2}x) \,dx\)
\(\int_{1}^{4}(\sqrt{x}-4x)\,dx \)
\(\int_{0}^{1}({\sqrt[5]{{t^{2}}}+1})\,dt \)
\(\int_{-2}^{3}[({x-1})\,(x+3)] \,{dx} \)
\(\int_{0}^{1}({z^{2}+1})^{2}dz\)
\(\int_{1}^{2}{\dfrac{x^{2}-12}{x^{4}}}\,dx \)
\(\int_{1}^{e}\dfrac{5s^{2}+s}{s^{2}}ds\)
\(\int_{1}^{4}\dfrac{x+1}{\sqrt{x}} dx\)
\(\int_{1}^{9}{\dfrac{\sqrt{x}+1}{x^{2}}} dx \)
\(\int_{1}^{2}{\dfrac{2{x^{4}+1}}{x^{4}}} dx\)
\(\int_{1}^{3}{\dfrac{2-x^{2}}{x^{4}}} dx \)
\(\int_{0}^{1/2}\left( 5+\dfrac{1}{\sqrt{1-x^{2}}} \right) dx\)
\(\int_{0}^{1}\left(1+\dfrac{5}{1+x^{2}}\right) dx\)
In Problems 33–38, use properties of integrals and the Fundamental Theorem of Calculus to find each integral.
\(\int_{-2}^{1}\,f(x)\,dx\), where \(f(x)={{\left\{ \begin{array}{c@{ }c@{ }c} 1 & \hbox{if} & x\lt0 \\ x^{2}+1 & \hbox{if} & x\geq 0 \end{array} \right.}}\)
\({{\int_{-1}^{-2}\,}}f(x)\,dx\), where \(f(x)={ {\left\{ \begin{array}{c@{ }c@{ }c} x+1 & \hbox{if} & x\lt0 \\ x^{2}+1 & \hbox{if} & x\geq 0 \end{array} \right.}}\)
\(\int_{-2}^{2}\,f(x)\,dx\), where \(f(x)={{\left\{ \begin{array}{c@{ }c@{ }c} 3x & \hbox{if} & -2\leq x\lt0 \\ 2x^{2} & \hbox{if} & 0\leq x\leq 2 \end{array} \right. }}\)
\(\int_{0}^{4}h(x)\,dx\), where \(h(x)={{\left\{ \begin{array}{c@{ }c@{ }c} x-2 & \hbox{if} & 0\leq x\leq 2 \\ 2-x & \hbox{if} & 2\lt x\leq 4 \end{array} \right. }}\)
\(\int_{-2}^{1}H(x)\,dx\), where \(H(x)={{\left\{ \begin{array}{c@{ }c@{ }c} 1+x^{2} & \hbox{if} & -2\leq x\lt0 \\ 1+3x & \hbox{if} & 0\leq x\leq 1 \end{array} \right. }}\)
\(\int_{-\pi /2}^{\pi /2}f(x)\,dx\), where \(f(x)=\left\{ \begin{array}{@{}l@{ }l@{ }l} {x^{2}+x} & \hbox{{if}} & {\ -{\dfrac{{\pi }}{{2}}}\leq x\leq 0} \\ {\sin x} & \hbox{{if}} & {0\lt x\lt{\dfrac{{\pi }}{{4}}}} \\ \dfrac{\sqrt{2}}{2} & \hbox{{if}} & {{\dfrac{{\pi }}{{4}}}\leq x\leq {\dfrac{{ \pi }}{{2}}}} \end{array} \right.\)
In Problems 39–42, the domain of \(f\) is a closed interval \([a,b]\). Find \(\int_{a}^{b}f(x) \,dx\).
In Problems 43–46, use properties of definite integrals to verify each statement. Assume that all integrals involved exist.
\(\int_{3}^{11}{f(x)\,dx-{\int_{7}^{11}{f(x)\,dx}}}=\int_{3}^{7}{f(x)\,dx}{}\)
\(\int_{-2}^{6}f(x)\,dx-{\int_{3}^{6}{f(x)\,dx}=\int_{-2}^{3}{f(x)\,dx}}\)
\(\int_{0}^{4}{f(x)\,dx-{\int_{6}^{4}}}f(x)\,dx=\int_{0}^{6}f(x)\,dx \)
\(\int_{-1}^{3}f(x)\,dx-{\int_{5}^{3}{f(x)\,dx=\int_{-1}^{5}{f(x)\,dx}}}\)
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In Problems 47–54, use the Bounds on an Integral Theorem to obtain a lower estimate and an upper estimate for each integral.
\(\int_{1}^{3}{({5x+1})\,dx} \)
\(\int_{0}^{1}{({1-x})\,dx} \)
\(\int_{\pi /4}^{\pi /2}{\sin x\,dx} \)
\(\int_{\pi /6}^{\pi /3}{\cos x\,dx}\)
\(\int_{0}^{1}{\sqrt{1+x^{2}}\,dx }\)
\(\int_{-1}^{1}{\sqrt{1+x^{4}}\,dx}\)
\(\int_{0}^{1}e^{x}dx\)
\(\int_{1}^{10}\dfrac{1}{x}dx \)
In Problems 55–60, for each integral find the number(s) \(u\) guaranteed by the Mean Value Theorem for Integrals.
\(\int_{0}^{3} (2{x^{2} + 1}) dx\)
\(\int_{0}^{2} (2-x^{3}) \,dx \)
\(\int_{0}^{4}x^{2}\,dx \)
\(\int_{0}^{4}(-x)\,dx \)
\(\int_{0}^{2\pi }\cos x\,dx \)
\(\int_{-\pi/4}^{\pi /4}\sec x\tan x dx\)
In Problems 61–70, find the average value of each function \(f\) over the given interval.
\(f(x) =e^{x}\) over \([0,1]\)
\(f(x) =\dfrac{1}{x}\) over \([1,e] \)
\(f(x) =x^{2/3}\) over \([-1,1] \)
\(f(x) =\sqrt{x}\) over \([0,4] \)
\(f(x) =\sin x\) over \(\left[0,\dfrac{{\pi }}{2}\right] \)
\(f(x) =\cos x\) over \(\left[ 0,\dfrac{{\pi }}{2} \right]\)
\(f(x) =1-x^{2}\) over \([-1,1] \)
\(f(x) =16-x^{2}\) over \([-4,\,4] \)
\(f(x) =e^{x}-{\sin x}\) over \(\left[0,\dfrac{\pi}{2}\right] \)
\(f(x) =x+\cos x\) over \(\left[0,\dfrac{{\pi }}{2}\right] \)
In Problems 71–74, find:
\([-1, 2]\)
\([-2, 1]\)
\([-1, 2]\)
\([0, \frac{3\pi}{4}]\)
Applications and Extensions
In Problems 75–78, find each definite integral using the Fundamental Theorem of Calculus and properties of definite integrals.
\(\int_{-2}^{3}{({x+{|x|}})\,dx}\)
\(\int_{0}^{3}{{|x-1|}\,dx} \)
\(\int_{0}^{2}{{|3x-1|}\,dx} \)
\(\int_{0}^{2}\vert {2-x} \vert dx\)
Average Temperature A rod \(3\) meters long is heated to \(25x^{\circ}{\rm C}\), where \(x\) is the distance in meters from one end of the rod. Find the average temperature of the rod.
Average Daily Rainfall The rainfall per day, \(x\) days after the beginning of the year, is modeled by the function \(r(x)=0.00002(6511+366x-x^{2}) \), measured in centimeters. Find the average daily rainfall for the first \(180\) days of the year.
Structural Engineering A structural engineer designing a member of a structure must consider the forces that will act on that member. Most often, natural forces like snow, wind, or rain distribute force over the entire member. For practical purposes, however, an engineer determines the distributed force as a single resultant force acting at one point on the member. If the distributed force is given by the function \(W=W(x)\), in newtons per meter (N/m), then the magnitude \(F_{R}\) of the resultant force is \[ F_{R}=\int_{a}^{b}W(x)\, dx \]
The position \(\bar{x}\) of the resultant force measured in meters from the origin is given by \[ \overline{x}=\dfrac{\int_{a}^{b}xW(x)\, dx}{\int_{a}^{b}W(x)\, dx} \]
If the distributed force is \(W(x) =0.75x^{3},\) \(0\leq x\leq 5,\) find:
source: Problem contributed by the students at Trine University, Avalon, IN.
Chemistry: Enthalpy In chemistry, enthalpy is a measure of the total energy of a system. For a nonreactive process with no phase change, the change in enthalpy \(\Delta H\) is given by \(\Delta H=\) \(\int_{T_{1}}^{T_{2}}C_{p}\, dT,\) where \(C_{p}\) is the specific heat of the system in question. The specific heat per mol of the chemical benzene is \[ C_{p} =0.126+(2.34\times 10^{-6}) T, \]
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where \(C_{p}\) is in \(kJ/\left(mol {}^{\circ}{\rm C} \right)\), and \(T\) is in degrees Celsius.
source: Problem contributed by the students at Trine University, Avalon, IN.
Average Mass Density The mass density of a metal bar of length \(3\) meters is given by \(\rho (x) = 1000 + x - \sqrt{x}\) kilograms per cubic meter, where \(x\) is the distance in meters from one end of the bar. What is the average mass density over the length of the entire bar?
Average Velocity The acceleration at time \(t\) of an object in rectilinear motion is given by \(a(t) =4\pi \cos t\). If the object's velocity is \(0\) at \(t = 0\), what is the average velocity of the object over the interval \(0\,\leq \,t\,\leq \,\pi \)?
Average Area What is the average area of all circles whose radii are between 1 and 3 m?
Area
Area
Area Let \(A\) be the area in the first quadrant that is enclosed by the graphs of \(y=3x^{2},\) \(y=\dfrac{3}{x},\) the \(x\)-axis, and the line \(x=k\), where \(k>1\), as shown in the figure.
Rectilinear Motion A car starting from rest accelerates at the rate of \(3\) m./s\(^{2}\). Find its average speed over the first 8 seconds.
Rectilinear Motion A car moving at a constant velocity of 80 miles per hour begins to decelerate at the rate of 10 mi/h\(^{2}\). Find its average speed over the next 10 minutes.
Average Slope
What theorem guarantees that the average slope found in Problem 91 is equal to \(f^{\prime }(u)\) for some \(u\) in \([a,b]?\) What different theorem guarantees the same thing? (Do you see the connection between these theorems?)
Prove that if a function \(f\) is continuous on a closed interval \([a,b]\) and if \(k\) is a constant, then \(\int_{a}^{b}kf(x)\,dx=k \int_{a}^{b}f(x)\,dx\).
Prove that if the functions \(f_{{1}}\), \(f_{{2}} , \ldots ,f_{n}\) are continuous on a closed interval \([a,b]\)and if \(k_{{1}}\), \(k_{{2}}, \ldots , k_{n}\) are constants, then \[ \begin{eqnarray*} &&\int_{a}^{b}[k_{{1}}f_{{1}}(x)+k_{{2}}f_{{2}}(x)+\cdots +k_{n}f_{n}(x)]\,dx \\ &&\enspace =k_{{1}}\int_{a}^{b}f_{{1}}(x)\,dx+k_{{2}}\int_{a}^{b}f_{{2}}(x)\,dx+\cdots + k_{n}\int_{a}^{b}f_{n}(x)\,dx \end{eqnarray*} \]
Area The area under the graph of \(y=\cos x\) from \(-\dfrac{\pi }{2}\) to \(\dfrac{\pi }{2}\) is separated into two parts by the line \(x=k\), \(\dfrac{-\pi}{2}\lt k \lt \dfrac{\pi}{2}\), as shown in the figure. If the area under the graph of \(y\) from \(-\dfrac{\pi }{2}\) to \(k\) is three times the area under the graph of \(y\) from \(k\) to \(\dfrac{\pi }{2},\) find \(k.\)
Displacement of a Damped Spring The displacement \(x\) in meters of a damped spring from its equilibrium position at time \(t\) seconds is given by \[ x(t) =\dfrac{\sqrt{15}}{10}e^{-t}\sin \big(\sqrt{15}t\big) + \dfrac{3}{2}e^{-t}\cos \big(\sqrt{15}t\big) \]
Area Let \[ f(x) =\vert x^{4}+3.44x^{3}-0.5041x^{2}-5.0882x +\,1.1523 \vert \]
be defined on the interval \([-3,1] \). Find the area under the graph of \(f.\)
If \(f\) is continuous on \([a,b]\), show that the functions defined by \[ F(x)= \int_{c}^{x}{f(t)\,dt} \qquad G(x)= \int_{d}^{x}{f(t)\,dt} \]
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for any choice of \(c\) and \(d\) in \((a,b)\) always differ by a constant. Also show that \[ F(x)-G(x)={\int_{c}^{d}{f(t)\,dt}} \]
Put It Together Suppose \(a\lt c\lt b\) and the function \(f\) is continuous on \([a,b]\) and differentiable on \((a,b)\). Which of the following is not necessarily true?
Minimizing Area Find \(b>0\) so that the area enclosed in the first quadrant by the graph of \(y=1+b-bx^2\) and the coordinate axes is a minimum.
Area Find the area enclosed by the graph of \(\sqrt{x}+\sqrt{y}=1\) and the coordinate axes.
Challenge Problems
Average Speed For a freely falling object starting from rest, \(v_{0}=0,\) find:
(Hint: The derivation of the formulas for freely falling objects is given in Section 4.8, pp. 334-337.)
Average Speed If an object falls from rest for 3 s, find:
Free Fall For a freely falling object starting from rest, \(v_{0}=0\), find:
Put It Together
Probability A function \(f\) that is continuous on the closed interval \([a,b],\) and for which (i) \(f(x)\geq 0\) for numbers \(x\) in \([a,b]\) and 0 elsewhere and (ii) \(\int_{a}^{b} f (x)\,dx=1,\) is called a probability density function. If \(a\leq c\lt d\leq b\), the probability of obtaining a value between \(c\) and \(d\) is defined as \(\int_{c}^{d}f(x)\,dx\).
Cumulative Probability Distribution Refer to Problem 106. If \(f\) is a probability density function the cumulative distribution function \(F\) for \(f\) is defined as \[ F(x)=\int_{a}^{x}f(t)\,dt \qquad a\leq x\leq b \]
Find the cumulative distribution function \(F\) for the probability density function \(f(x) =kx\) of Problem 106(a).
For the cumulative distribution function \(F(x)=x-1\), on the interval \([1,2]\):
Let \(f(x)=x^{3}-6x^{2}+11x-6\). Find \(\int_{1}^{3}\vert f(x)\vert dx.\)
Show that for \(x>1,\) \(\ln x\lt2 (\sqrt{x}-1).\)
(Hint: Use the result given on Problem 114.)
Prove that the average value of a line segment \(y=m (x-x_{1} ) +y_{1}\) on the interval \([x_{1},x_{2}]\) equals the \(y\)-coordinate of the midpoint of the line segment from \(x_{1}\) to \(x_{2}.\)
Prove that if a function \(f\) is continuous on a closed interval \([a,b]\) and if \(f(x)\geq 0\) on \([a,b]\), then \(\int_{a}^{b}f(x)\,dx \geq 0\).
Prove that if functions \(f\) and \(g\) are continuous on a closed interval \([a,b]\) and if \(f(x)\geq \,g(x)\) on \([a,b]\), then \[ \int_{a}^{b}f(x)\,dx\geq \int_{a}^{b}g(x)\,dx. \]
Prove that if \(f\) is continuous on \([a,b]\), then \[ \left\vert \int_{a}^{b} f(x)\,dx\right\vert \leq \int_{a}^{b}\vert {f(x)}\vert\, dx. \]
Give a geometric interpretation of the inequality.