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Concepts and Vocabulary
If the substitution \(u=2x+3\) is used with \(\int \sin (2x+3)\, dx,\) the result is \(\int\) _________\(du.\)
True or False If the substitution \(u=x^{2}+3\) is used with \(\int_{0}^{1}x(x^{2}+3)^{3}dx,\) the result is \(\int_{0}^{1}x(x^{2}+3) ^{3}dx=\dfrac{1}{2}\int_{0}^{1}u^{3}du.\)
Multiple Choice \(\int_{-4}^{4}x^{3}dx= [{\boldsymbol (a)}\, 128\enspace {\boldsymbol (b)}\, 4\enspace {\boldsymbol (c)}\,0\enspace {\boldsymbol (d)}\,64 ]\).
True or False \(\int_{0}^{5}x^{2}dx=\dfrac{1}{2}\int_{-5}^{5}x^{2}dx\).
Skill Building
In Problems 5–10, find each indefinite integral using the given substitution.
\(\int e^{3x+1}dx\); let \(u=3x+1\).
\(\int \dfrac{dx}{x\ln x}\); let \(u=\ln x\).
\(\int {({1-t^{2}})^{6}t\,dt};\) let \(u=1-t^{2} \).
\(\int {\sin ^{5}x\cos x\,dx;}\) let \(u=\sin x \).
\(\int \dfrac{x^{2}\,dx}{\sqrt{1-x^{6}}}\ ;\) let \(u=x^{3}\).
\(\int \dfrac{e^{-x}}{6+e^{-x}} dx;\) let \(u=6+e^{-x}\).
In Problems 11–44, find each indefinite integral.
\(\int \sin (3x) \,dx\)
\(\int {x}\sin x^{2}\,dx\)
\(\int {\sin x\cos^{2}x\,dx}\)
\(\int \tan ^{2}x\sec ^{2}x\,dx \)
\(\int \dfrac{e^{1/x}}{x^{2}} dx\)
\(\int \dfrac{e^{\sqrt[3]{x}}}{\sqrt[3]{x^{2}}} dx\)
\(\int \dfrac{x\;dx}{x^{2}-1}\)
\(\int \dfrac{5x\;dx}{1-x^{2}}\)
\(\int \dfrac{e^{x}}{\sqrt{1+e^{x}}} dx\)
\(\int \dfrac{dx}{x(\ln x)^{7}}\)
\(\int {{\dfrac{1}{{\sqrt{x}( {1+\sqrt{x}})^{4}}}}\,dx}\)
\(\int \dfrac{dx}{\sqrt{x}(1+\sqrt{x})}\)
\(\int \dfrac{3e^{x}}{\sqrt[4]{e^{x}-1}} dx\)
\(\int \dfrac{[ \ln ( 5x) ] ^{3}}{x} dx\)
\(\int \dfrac{\cos x\;dx}{2\sin x-1}\)
\(\int \dfrac{\cos (2x)\;dx}{\sin (2x)} \)
\(\int \sec (5x) \,dx\)
\(\int \tan (2x) \,dx\)
\(\int \sqrt{\tan x}\sec^{2}x\,dx\)
\(\int (2+3\cot x)^{3/2}\csc^{2}x\,dx\)
\(\int \dfrac{\sin x}{\cos ^{2}x}\,dx\)
\(\int \dfrac{\cos x}{\sin ^{2}x}\,dx\)
\(\int \sin x\cdot e^{\cos x}\,dx\)
\(\int \sec ^{2}x\cdot e^{\tan x}\,dx\)
\(\int {x\sqrt{x+3}\,dx}\)
\(\int {x\sqrt{4-x}\,dx}\)
\(\int\, [ \sin x+\cos (3x) ] dx\)
\(\int\, \Big[ x^{2}+\sqrt{3x+2}\Big] dx\)
\(\int \dfrac{dx}{x^{2}+25}\)
\(\int \dfrac{\cos x}{1+\sin ^{2}x}\,dx\)
\(\int \dfrac{dx}{\sqrt{9-x^{2}}}\)
\(\int \dfrac{dx}{\sqrt{16-9x^{2}}} \)
\(\int \sinh x\cosh x\,dx\)
\(\int \hbox{ sech}^{2}x\tanh x\,dx \)
In Problems 45–52, find each definite integral two ways:
\(\int_{-2}^{0}\dfrac{x}{(x^{2}+3)^{2}} dx\)
\(\int_{-1}^{1}( s^{2}-1) ^{5}s ds\)
\(\int_{0}^{1}x^{2}e^{x^{3}+1} dx\)
\(\int_{0}^{1}xe^{x^{2}-2} dx\)
\(\int_{1}^{6}x\sqrt{x+3}\,dx \)
\(\int_{2}^{6}x^{2}\sqrt{x-2} dx\)
\(\int_{0}^{2}x\cdot 3^{2x^{2}} dx\)
\(\int_{0}^{1}x\cdot 10^{-x^{2}} dx\)
In Problems 53–62, find each definite integral.
\(\int_{1}^{3}\dfrac{1}{x^{2}}\sqrt{1-\dfrac{1}{x}} dx\)
\(\int_{0}^{\pi /4}\dfrac{\sin (2x)}{\sqrt{5-2\cos (2x) }} dx\)
\(\int_{0}^{2}\dfrac{e^{2x}}{e^{2x}+1} dx \)
\(\int_{1}^{3}\dfrac{e^{3x}}{e^{3x}-1} dx\)
\(\int_{2}^{3}\dfrac{dx}{x\ln x}\)
\(\int_{2}^{3}\dfrac{dx}{x(\ln x)^{2}}\)
\(\int_{0}^{\pi }e^{x}\cos (e^{x}) \,dx\)
\(\int_{0}^{\pi }e^{-x}\cos (e^{-x}) \,dx\)
\(\int_{0}^{1}\dfrac{x\,dx}{1+x^{4}}\)
\(\int_{0}^{1}\dfrac{e^{x}}{1+e^{2x}} dx\)
In Problems 63–70, use properties of integrals to find each integral.
\(\int_{-2}^{2}( x^{2}-4) dx\)
\(\int_{-1}^{1}( x^{3}-2x) dx\)
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\(\int_{-\pi /2}^{\pi /2}\dfrac{1}{3}\sin \theta d\theta \)
\(\int_{-\pi /4}^{\pi /4}\sec^{2}x\,dx\)
\(\int_{-1}^{1}\dfrac{3}{1+x^{2}}\,dx \)
\({{\int_{-5}^{5}}} \big(x^{1/3}+x\big){ dx}\)
\(\int_{-5}^{5}\vert 2x\vert \,dx\)
\(\int_{-1}^{1}[\vert x\vert -3 ] \,dx\)
Applications and Extensions
In Problems 71–84, find each integral.
\(\int \dfrac{x+1}{x^{2}+1}dx\)
\(\int \dfrac{2x-3}{1+x^{2}}dx \)
\(\int \left({2\sqrt{x^{2}+3}-{\dfrac{{4}}{{x}}}+9}\right) ^{6}\left({{\dfrac{{x}}{\sqrt{x^{2}+3}}}+{\dfrac{{2}}{{x^{2}}}}}\right) dx\)
\(\int {{\Big[\sqrt{({z^{2}+1})^{4}-3}\Big]}{\Big[z{({z^{2}+1})^{3}}\Big]}\,dz}\)
\(\int {{\dfrac{{x+4x^{3}}}{\sqrt{x}}}\,dx}\)
\(\int {{\dfrac{{z\,dz}}{{z+\sqrt{z^{2}+4}}}}}\)
\(\int {\sqrt{t}\sqrt{4+t\sqrt{t}}\,dt } \)
\(\int_{0}^{1}\dfrac{x+1}{x^{2}+3}dx\)
\(\int 3^{2x+1}dx\)
\(\int 2^{3x+5}dx\)
\(\int \dfrac{\sin x}{\sqrt{4-\cos ^{2}x}}dx\)
\(\int \dfrac{\sec^{2}x\,dx}{\sqrt{1-\tan^{2}x}}\)
\(\int_{0}^{1}\dfrac{(z^{2}+5)(z^{3}+15z-3)\,}{{196-(z^{3}+15z-3)^{2}}}dz\)
\(\int_{2}^{17}\dfrac{dx}{\sqrt{\sqrt{{x-1}}+(x-1)^{5/4}}}\)
In Problems 85–90, find each integral. (Hint: Begin by using a Change of Base formula.)
\(\int \dfrac{dx}{x\log _{10}x}\)
\(\int \dfrac{dx}{x\log _{3}\sqrt[5]{x}}\)
\(\int_{10}^{100}\dfrac{dx}{x\log x}\)
\(\int_{3}^{32}\dfrac{dx}{x\log_2 x}\)
\(\int_{3}^{9}\dfrac{dx}{x\log _{3}x} \)
\(\int_{10}^{100}\dfrac{dx}{x\log _{5}x} \)
If \(\int_{1}^{b}t^{2}(5t^{3}-1)^{1/2}\,dt=\dfrac{38}{45},\) find \(b.\)
If \(\int_{a}^{3}t\sqrt{9-t^{2}}\,dt=6,\) find \(a.\)
In Problems 93 and 94, find each indefinite integral by:
\(\int (x+1) ^{2} dx\)
\(\int ( x^{2}+1) ^{2}x\, dx\)
In Problems 95 and 96, find each integral three ways:
\(\int_{-\pi /2}^{\pi /2}\,\cos (2x+\pi )\,dx \)
\(\int_{{-}\pi /4}^{\pi /4}\sin ( 7\theta -\pi)\,d\theta \)
Area Find the area under the graph of \(f(x) =\dfrac{x^{2}}{\sqrt{2x+1}}\) from \(0\) to \(4.\)
Area Find the area under the graph of \(f(x) =\dfrac{x}{(x^{2}+1) ^{2}}\) from \(0\) to \(2.\)
Area Find the area under the graph of \(y=\dfrac{1}{3x^{2}+1}\) from \(x=0\) to \(x=1\).
Area Find the area under the graph of \(y=\dfrac{1}{x\sqrt{x^{2}-4}}\) from \(x=3\) to \(x=4\).
Area Find the area under the graph of the catenary, \[ y=a\cosh \dfrac{x}{a}+b-a, \]
from \(x=0\) to \(x=a\).
Area Find \(b\) so that the area under the graph of \[ y=(x+1)\sqrt{x^{2}+2x+4} \]
is \(\dfrac{56}{3}\) for \(0\leq x\leq b\).
Average Value Find the average value of \(y=\tan x\) on the interval \(\left[ 0,\dfrac{\pi }{4}\right] \).
Average Value Find the average value of \(y=\sec x\) on the interval \(\left[ 0,\dfrac{\pi}{4}\right] \).
If \(\int_{0}^{2}f(x - 3)\,dx = 8\), find \({\int_{-3}^{-1}{f(x)\,dx. }} \)
If \(\int_{-2}^{1}f(x + 1)\,dx=\dfrac{5}{2}\), find \({\int_{-1}^{2}{f(x)\,dx.}}\)
If \(\int_{0}^{4}f\left( \dfrac{x}{2}\right) dx = 8\), find \({\int_{0}^{2}{f(x)\,dx.}}\)
If \(\int_{0}^{1}g(3x)\,dx = 6\), find \({\int_{0}^{3}}g{(x)\,dx.}\)
Newton's Law of Cooling Newton's Law of Cooling states that the rate of change of temperature with respect to time is proportional to the difference between the temperature of the object and the ambient temperature. A thermometer that reads \(4{}^{\circ}{\rm C}\) is brought into a room that is \(30{}^{\circ}{\rm C}\).
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Newton's Law of Cooling A thermometer reading \(70{}^{\circ}{\rm F}\) is taken outside where the ambient temperature is \(22{}^{\circ}{\rm F}\). Four minutes later the reading is \(32{}^{\circ}{\rm F}\).
Forensic Science At \(4\) p.m., a body was found floating in water whose temperature is \(12{}^{\circ}{\rm C}.\) When the woman was alive, her body temperature was \(37{}^{\circ}{\rm C}\) and now it is \(20{}^{\circ}{\rm C}.\) Suppose the rate of change of the temperature \(u =u(t)\) of the body with respect to the time \(t\) in hours (h) is proportional to \(u(t)-T\), where \(T\) is the water temperature and the constant of proportionality is \(-0.159.\)
Newton's Law of Cooling A pie is removed from a \(350{}^{\circ}{\rm F}\) oven to cool in a room whose temperature is \(72{}^{\circ}{\rm F}\).
Electric Potential The electric field strength a distance \(z \) from the axis of a ring of radius \(R\) carrying a charge \(Q\) is given by the formula \[ E(z)={\dfrac{{Qz}}{{(R^{2}+z^{2})^{3/2}}}} \]
If the electric potential \(V\) is related to \(E\) by \(E=-\dfrac{dV}{dz}\), what is \(V(z)\)?
Impulse During a Rocket Launch The impulse \(J\) due to a force \(F\) is the product of the force times the amount of time \(t\) for which the force acts. When the force varies over time, \[ J=\int_{t_{1}}^{t_{2}}F(t)\,dt. \]
We can model the force acting on a rocket during launch by an exponential function \(F(t)=Ae^{bt}\), where \(A\) and \(b\) are constants that depend on the characteristics of the engine. At the instant lift-off occurs (\(t=0\)), the force must equal the weight of the rocket.
Air Resistance on a Falling Object If an object of mass \(m\) is dropped, the air resistance on it when it has speed \(v\) can be modeled as \(F_{{\rm air}}=-kv\), where the constant \(k\) depends on the shape of the object and the condition of the air. The minus sign is necessary because the direction of the force is opposite to the velocity. Using Newton's Second Law of Motion, this force leads to a downward acceleration \(a(t)=ge^{-kt/m} \). See Problem 137. Using the equation for \(a(t)\), find:
Area Let \(f(x)=k\sin ( kx) \), where \(k\) is a positive constant.
Use an appropriate substitution to show that \[ \int_{0}^{1}x^{m}(1 - x)^{n} dx = \int_{0}^{1}x^{n}(1 - x)^{m} dx, \]
where \(m,\) \(n\) are positive integers.
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Properties of Integrals Find \({\int_{-1}^{1}{f(x)\,dx}}\) for the function given below: \[ f(x)={\left\{ {{ \begin{array}{l@{ }l@{ }l} {x+1} & \hbox{if} & {x\lt0} \\ \cos (\pi x) & \hbox{if} & {x\geq 0} \end{array} }}\right. } \]
If \(f\) is continuous on \([a,b]\), show that \[ \int_{a}^{b}f(x)\,dx = \int_{a}^{b}f(a + b -\,x)\,dx \]
If \(\int_{0}^{1}f(x) \,dx = 2\), find:
If \(\int_{0}^{2}f (s) \,ds = 5\), find:
Find \(\int_{0}^{b}\vert 2x\vert \,dx\) for any real number \(b.\)
If \(f\) is an odd function, show that \(\int_{-a}^{a}f(x)\,dx = 0\).
Find the constant \(k\), where \(0\leq k\leq \,3\), for which \[ {\int_{0}^{3}{{\dfrac{{x}}{\sqrt{x^{2}+16}}}dx={\dfrac{{3k}}{\sqrt{k^{2}+16}}} }} \]
If \(n\) is a positive integer, for what number is \[ \int_{0}^{a}x^{n-1} dx= \dfrac{1}{n} \]
If \(f\) is a continuous function defined on the interval \([0,1]\), show that \[ {\int_{0}^{\pi }{x f(\sin x)\,dx={\dfrac{{\pi }}{{2}}}{\int_{0}^{\pi }{f(\sin x)\,dx}}}} \]
Prove that \(\int \csc x\,dx=\ln \left\vert \csc x-\cot x\right\vert +C\). [Hint: Multiply and divide the integrand by \((\csc x-\cot x)\).]
Describe a method for finding \(\int_{a}^{b}\vert f(x)\vert \,dx\) in terms of \(F(x)=\int f(x)\mathit{~}dx\) when \(f(x)\) has finitely many zeros.
Find \(\int \sqrt[n]{{a\,{+}\,bx}}\,dx\), where \(a\) and \(b\) are real numbers, \(b\neq 0\), and \(n\geq 2\) is an integer.
If \(f\) is continuous for all \(x\), which of the following integrals have the same value?
Challenge Problems
Find \(\int {{\dfrac{{x^{6}+3x^{4}+3x^{2}+x+1}}{{(x^{2}+1)^{2}}}}}\,dx\).
Find \(\int \dfrac{\sqrt[4]{x}}{\sqrt{x}+\sqrt[3]{x}}dx\).
Find \(\int \dfrac{3x+2}{x\sqrt{x+1}}\ dx\).
Find \(\int \dfrac{dx}{(x\ln x) [\ln (\ln x)] }\).
Air Resistance on a Falling Object (Refer to Problem 115.) If an object of mass \(m\) is dropped, the air resistance on it when it has speed \(v\) can be modeled as \[ F_{{\rm air}}=-kv, \]
where the constant \(k\) depends on the shape of the object and the condition of the air. The minus sign is necessary because the direction of the force is opposite to the velocity. Using Newton's Second Law of Motion, show that the downward acceleration of the object is \[ a(t) =ge^{-kt/m}, \]
where \(g\) is the acceleration due to gravity. (Hint: The velocity of the object obeys the differential equation \[ m\dfrac{dv}{dt}=mg-kv \]
Solve the differential equation for \(v\) and use the fact that \(ma=mg-kv\).)
A separable differential equation can be written in the form \(\dfrac{dy}{dx}=\dfrac{f(x)}{g (y)}\), where \(f\) and \(g\) are continuous. Then \[ \int g(y)\,dy=\int f(x)\,dx \]
and integrating (if possible) will give a solution to the differential equation. Use this technique to solve parts (a)–(c) below. (You may need to leave your answer in implicit form.)