5.6 Assess Your Understanding

396

Concepts and Vocabulary

Question

If the substitution \(u=2x+3\) is used with \(\int \sin (2x+3)\, dx,\) the result is \(\int\) _________\(du.\)

Question

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 \(\int_{0}^{1}x(x^{2}+3) ^{3}dx=\dfrac{1}{2}\int_{0}^{1}u^{3}du.\)

Question

Multiple Choice  \(\int_{-4}^{4}x^{3}dx= [{\boldsymbol (a)}\, 128\enspace {\boldsymbol (b)}\, 4\enspace {\boldsymbol (c)}\,0\enspace {\boldsymbol (d)}\,64 ]\).

Question

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.

Question

\(\int e^{3x+1}dx\); let \(u=3x+1\).

Question

\(\int \dfrac{dx}{x\ln x}\); let \(u=\ln x\).

Question

\(\int {({1-t^{2}})^{6}t\,dt};\) let \(u=1-t^{2} \).

Question

\(\int {\sin ^{5}x\cos x\,dx;}\) let \(u=\sin x \).

Question

\(\int \dfrac{x^{2}\,dx}{\sqrt{1-x^{6}}}\ ;\) let \(u=x^{3}\).

Question

\(\int \dfrac{e^{-x}}{6+e^{-x}} dx;\) let \(u=6+e^{-x}\).

In Problems 11–44, find each indefinite integral.

Question

\(\int \sin (3x) \,dx\)

Question

\(\int {x}\sin x^{2}\,dx\)

Question

\(\int {\sin x\cos^{2}x\,dx}\)

Question

\(\int \tan ^{2}x\sec ^{2}x\,dx \)

Question

\(\int \dfrac{e^{1/x}}{x^{2}} dx\)

Question

\(\int \dfrac{e^{\sqrt[3]{x}}}{\sqrt[3]{x^{2}}} dx\)

Question

\(\int \dfrac{x\;dx}{x^{2}-1}\)

Question

\(\int \dfrac{5x\;dx}{1-x^{2}}\)

Question

\(\int \dfrac{e^{x}}{\sqrt{1+e^{x}}} dx\)

Question

\(\int \dfrac{dx}{x(\ln x)^{7}}\)

Question

\(\int {{\dfrac{1}{{\sqrt{x}( {1+\sqrt{x}})^{4}}}}\,dx}\)

Question

\(\int \dfrac{dx}{\sqrt{x}(1+\sqrt{x})}\)

Question

\(\int \dfrac{3e^{x}}{\sqrt[4]{e^{x}-1}} dx\)

Question

\(\int \dfrac{[ \ln ( 5x) ] ^{3}}{x} dx\)

Question

\(\int \dfrac{\cos x\;dx}{2\sin x-1}\)

Question

\(\int \dfrac{\cos (2x)\;dx}{\sin (2x)} \)

Question

\(\int \sec (5x) \,dx\)

Question

\(\int \tan (2x) \,dx\)

Question

\(\int \sqrt{\tan x}\sec^{2}x\,dx\)

Question

\(\int (2+3\cot x)^{3/2}\csc^{2}x\,dx\)

Question

\(\int \dfrac{\sin x}{\cos ^{2}x}\,dx\)

Question

\(\int \dfrac{\cos x}{\sin ^{2}x}\,dx\)

Question

\(\int \sin x\cdot e^{\cos x}\,dx\)

Question

\(\int \sec ^{2}x\cdot e^{\tan x}\,dx\)

Question

\(\int {x\sqrt{x+3}\,dx}\)

Question

\(\int {x\sqrt{4-x}\,dx}\)

Question

\(\int\, [ \sin x+\cos (3x) ] dx\)

Question

\(\int\, \Big[ x^{2}+\sqrt{3x+2}\Big] dx\)

Question

\(\int \dfrac{dx}{x^{2}+25}\)

Question

\(\int \dfrac{\cos x}{1+\sin ^{2}x}\,dx\)

Question

\(\int \dfrac{dx}{\sqrt{9-x^{2}}}\)

Question

\(\int \dfrac{dx}{\sqrt{16-9x^{2}}} \)

Question

\(\int \sinh x\cosh x\,dx\)

Question

\(\int \hbox{ sech}^{2}x\tanh x\,dx \)

In Problems 45–52, find each definite integral two ways:

  1. By finding the related indefinite integral and then using the Fundamental Theorem of Calculus.
  2. By making a substitution in the integrand and using the substitution to change the limits of integration.
  3. Which method did you prefer? Why?

Question

\(\int_{-2}^{0}\dfrac{x}{(x^{2}+3)^{2}} dx\)

Question

\(\int_{-1}^{1}( s^{2}-1) ^{5}s ds\)

Question

\(\int_{0}^{1}x^{2}e^{x^{3}+1} dx\)

Question

\(\int_{0}^{1}xe^{x^{2}-2} dx\)

Question

\(\int_{1}^{6}x\sqrt{x+3}\,dx \)

Question

\(\int_{2}^{6}x^{2}\sqrt{x-2} dx\)

Question

\(\int_{0}^{2}x\cdot 3^{2x^{2}} dx\)

Question

\(\int_{0}^{1}x\cdot 10^{-x^{2}} dx\)

In Problems 53–62, find each definite integral.

Question

\(\int_{1}^{3}\dfrac{1}{x^{2}}\sqrt{1-\dfrac{1}{x}} dx\)

Question

\(\int_{0}^{\pi /4}\dfrac{\sin (2x)}{\sqrt{5-2\cos (2x) }} dx\)

Question

\(\int_{0}^{2}\dfrac{e^{2x}}{e^{2x}+1} dx \)

Question

\(\int_{1}^{3}\dfrac{e^{3x}}{e^{3x}-1} dx\)

Question

\(\int_{2}^{3}\dfrac{dx}{x\ln x}\)

Question

\(\int_{2}^{3}\dfrac{dx}{x(\ln x)^{2}}\)

Question

\(\int_{0}^{\pi }e^{x}\cos (e^{x}) \,dx\)

Question

\(\int_{0}^{\pi }e^{-x}\cos (e^{-x}) \,dx\)

Question

\(\int_{0}^{1}\dfrac{x\,dx}{1+x^{4}}\)

Question

\(\int_{0}^{1}\dfrac{e^{x}}{1+e^{2x}} dx\)

In Problems 63–70, use properties of integrals to find each integral.

Question

\(\int_{-2}^{2}( x^{2}-4) dx\)

Question

\(\int_{-1}^{1}( x^{3}-2x) dx\)

397

Question

\(\int_{-\pi /2}^{\pi /2}\dfrac{1}{3}\sin \theta d\theta \)

Question

\(\int_{-\pi /4}^{\pi /4}\sec^{2}x\,dx\)

Question

\(\int_{-1}^{1}\dfrac{3}{1+x^{2}}\,dx \)

Question

\({{\int_{-5}^{5}}} \big(x^{1/3}+x\big){ dx}\)

Question

\(\int_{-5}^{5}\vert 2x\vert \,dx\)

Question

\(\int_{-1}^{1}[\vert x\vert -3 ] \,dx\)

Applications and Extensions

In Problems 71–84, find each integral.

Question

\(\int \dfrac{x+1}{x^{2}+1}dx\)

Question

\(\int \dfrac{2x-3}{1+x^{2}}dx \)

Question

\(\int \left({2\sqrt{x^{2}+3}-{\dfrac{{4}}{{x}}}+9}\right) ^{6}\left({{\dfrac{{x}}{\sqrt{x^{2}+3}}}+{\dfrac{{2}}{{x^{2}}}}}\right) dx\)

Question

\(\int {{\Big[\sqrt{({z^{2}+1})^{4}-3}\Big]}{\Big[z{({z^{2}+1})^{3}}\Big]}\,dz}\)

Question

\(\int {{\dfrac{{x+4x^{3}}}{\sqrt{x}}}\,dx}\)

Question

\(\int {{\dfrac{{z\,dz}}{{z+\sqrt{z^{2}+4}}}}}\)

Question

\(\int {\sqrt{t}\sqrt{4+t\sqrt{t}}\,dt } \)

Question

\(\int_{0}^{1}\dfrac{x+1}{x^{2}+3}dx\)

Question

\(\int 3^{2x+1}dx\)

Question

\(\int 2^{3x+5}dx\)

Question

\(\int \dfrac{\sin x}{\sqrt{4-\cos ^{2}x}}dx\)

Question

\(\int \dfrac{\sec^{2}x\,dx}{\sqrt{1-\tan^{2}x}}\)

Question

\(\int_{0}^{1}\dfrac{(z^{2}+5)(z^{3}+15z-3)\,}{{196-(z^{3}+15z-3)^{2}}}dz\)

Question

\(\int_{2}^{17}\dfrac{dx}{\sqrt{\sqrt{{x-1}}+(x-1)^{5/4}}}\)

In Problems 85–90, find each integral. (Hint: Begin by using a Change of Base formula.)

Question

\(\int \dfrac{dx}{x\log _{10}x}\)

Question

\(\int \dfrac{dx}{x\log _{3}\sqrt[5]{x}}\)

Question

\(\int_{10}^{100}\dfrac{dx}{x\log x}\)

Question

\(\int_{3}^{32}\dfrac{dx}{x\log_2 x}\)

Question

\(\int_{3}^{9}\dfrac{dx}{x\log _{3}x} \)

Question

\(\int_{10}^{100}\dfrac{dx}{x\log _{5}x} \)

Question

If \(\int_{1}^{b}t^{2}(5t^{3}-1)^{1/2}\,dt=\dfrac{38}{45},\) find \(b.\)

Question

If \(\int_{a}^{3}t\sqrt{9-t^{2}}\,dt=6,\) find \(a.\)

In Problems 93 and 94, find each indefinite integral by:

  1. First using substitution.
  2. First expanding the integrand.

Question

\(\int (x+1) ^{2} dx\)

Question

\(\int ( x^{2}+1) ^{2}x\, dx\)

In Problems 95 and 96, find each integral three ways:

  1. By using substitution.
  2. By using properties of the definite integral.
  3. By using trigonometry to simplify the integrand before integrating.
  4. Compare the results.

Question

\(\int_{-\pi /2}^{\pi /2}\,\cos (2x+\pi )\,dx \)

Question

\(\int_{{-}\pi /4}^{\pi /4}\sin ( 7\theta -\pi)\,d\theta \)

Question

Area  Find the area under the graph of \(f(x) =\dfrac{x^{2}}{\sqrt{2x+1}}\) from \(0\) to \(4.\)

Question

Area  Find the area under the graph of \(f(x) =\dfrac{x}{(x^{2}+1) ^{2}}\) from \(0\) to \(2.\)

Question

Area  Find the area under the graph of \(y=\dfrac{1}{3x^{2}+1}\) from \(x=0\) to \(x=1\).

Question

Area  Find the area under the graph of \(y=\dfrac{1}{x\sqrt{x^{2}-4}}\) from \(x=3\) to \(x=4\).

Question

Area  Find the area under the graph of the catenary, \[ y=a\cosh \dfrac{x}{a}+b-a, \]

from \(x=0\) to \(x=a\).

Question

Area  Find \(b\) so that the area under the graph of \[ y=(x+1)\sqrt{x^{2}+2x+4} \]

is \(\dfrac{56}{3}\) for \(0\leq x\leq b\).

Question

Average Value  Find the average value of \(y=\tan x\) on the interval \(\left[ 0,\dfrac{\pi }{4}\right] \).

Question

Average Value  Find the average value of \(y=\sec x\) on the interval \(\left[ 0,\dfrac{\pi}{4}\right] \).

Question

If \(\int_{0}^{2}f(x - 3)\,dx = 8\), find \({\int_{-3}^{-1}{f(x)\,dx. }} \)

Question

If \(\int_{-2}^{1}f(x + 1)\,dx=\dfrac{5}{2}\), find \({\int_{-1}^{2}{f(x)\,dx.}}\)

Question

If \(\int_{0}^{4}f\left( \dfrac{x}{2}\right) dx = 8\), find \({\int_{0}^{2}{f(x)\,dx.}}\)

Question

If \(\int_{0}^{1}g(3x)\,dx = 6\), find \({\int_{0}^{3}}g{(x)\,dx.}\)

Question

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 \(30{}^{\circ}{\rm C}\).

  1. Write the differential equation that models the temperature \(u=u(t) \) of the thermometer at time \(t\) in minutes (min).
  2. Find the general solution of the differential equation.
  3. If the thermometer reads \(10{}^{\circ}{\rm C}\) after 2 min, determine the temperature reading 5 min after the thermometer is first brought into the room.

398

Question

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 \(32{}^{\circ}{\rm F}\).

  1. Write the differential equation that models the temperature \(u=u(t) \) of the thermometer at time \(t.\)
  2. Find the general solution of the differential equation.
  3. Find the particular solution to the differential equation, using the initial condition that when \(t = 0\) min, then \(u=70{}^{\circ}{\rm F}.\)
  4. Find the thermometer reading 7 min after the thermometer was brought outside.
  5. Find the time it takes for the reading to change from \(70{}^{\circ}{\rm F}\) to within \(\dfrac{1}{2}{}^{\circ}{\rm F}\) of the air temperature.

Question

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 \(-0.159.\)

  1. Write a differential equation that models the temperature \(u=u(t) \) of the body at time \(t\).
  2. Find the general solution of the differential equation.
  3. Find the particular solution to the differential equation, using the initial condition that at the time of death, when \(t=0 h\), her body temperature was \(u=37{}^{\circ}{\rm C}.\)
  4. At what time did the woman drown?
  5. How long does it take for the woman's body to cool to 15\(^{\circ}\)C?

Question

Newton's Law of Cooling  A pie is removed from a \(350{}^{\circ}{\rm F}\) oven to cool in a room whose temperature is \(72{}^{\circ}{\rm F}\).

  1. Write the differential equation that models the temperature \(u=u(t) \) of the pie at time \(t.\)
  2. Find the general solution of the differential equation.
  3. Find the particular solution to the differential equation, using the initial condition that when \(t=0 min\), then \(u=350{}^{\circ}{\rm F}.\)
  4. If \(u(5) =\) \(200{}^{\circ}{\rm F},\) what is the temperature of the pie after \(15\) min?
  5. How long will it take for the pie to be \(100{}^{\circ}{\rm F}\) and ready to eat?

Question

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 \(V(z)\)?

Question

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.

  1. Suppose the rocket weighs 25,000 N (a mass of about 2500 kg or a weight of 5500lb), and 30 seconds after lift-off the force acting on the rocket equals twice the weight of the rocket. Find \(A\) and \(b.\)
  2. Find the impulse delivered to the rocket during the first 30 seconds after the launch.

Question

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:

  1. \(v(t)\), if the object starts from rest \(v_0=v(0)=0\), with the positive direction downward.
  2. \(s(t)\), if the object starts from the position \(s_0=s(0)=0\), with the positive direction downward.
  3. What limits do \(a(t)\), \(v(t)\), and \(s(t)\) approach if the object falls for a very long time (\(t\rightarrow \infty \))? Interpret each result and explain if it is physically reasonable.
  4. Graph \(a=a(t)\), \(v=v(t)\), \(s=s(t)\). Do the graphs support the conclusions obtained in part (c)? Use \(g = 9.8\) m\(/\)s\(^2\), \(k = 5\), and \(m = 10\) kg.

Question

Area  Let \(f(x)=k\sin ( kx) \), where \(k\) is a positive constant.

  1. Find the area of the region under one arch of the graph of \(f.\)
  2. Find the area of the triangle formed by the \(x\)-axis and the tangent lines to one arch of \(f\) at the points where the graph of \(f\) crosses the \(x\)-axis.

Question

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.

399

Question

Properties of Integrals  Find \({\int_{-1}^{1}{f(x)\,dx}}\) for the function given below: \[ f(x)={\left\{ {{ \begin{array}{l@{ }l@{ }l} {x+1} & \hbox{if} & {x\lt0} \\ \cos (\pi x) & \hbox{if} & {x\geq 0} \end{array} }}\right. } \]

Question

If \(f\) is continuous on \([a,b]\), show that \[ \int_{a}^{b}f(x)\,dx = \int_{a}^{b}f(a + b -\,x)\,dx \]

Question

If \(\int_{0}^{1}f(x) \,dx = 2\), find:

  1. \({\int_{0}^{0.5}{f(2x)\,dx }} \)
  2. \(\int_{0}^{3}f \left( \dfrac{1}{3}x\right) dx\)
  3. \(\int_{0}^{1/5}f( 5x) dx\)
  4. Find the upper and lower limits of integration so that \[ \int_{a}^{b}f\left( \dfrac{x}{4}\right) dx=8. \]
  5. Generalize (d) so that \(\int_{a}^{b}f( kx) dx=\dfrac{1}{k}\cdot 2\) for \(k>0.\)

Question

If \(\int_{0}^{2}f (s) \,ds = 5\), find:

  1. \({\int_{-1}^{1}{f(s+1)\,ds }}\)
  2. \(\int_{-3}^{-1}f( s+3) \,ds\)
  3. \(\int_{4}^{6}f( s-4) \,ds\)
  4. Find the upper and lower limits of integration so that \[ \int_{a}^{b}f(s - 2) ds=5. \]
  5. Generalize (d) so that \(\int_{a}^{b}f( s-k) \,ds=5\) for \(k>0.\)

Question

Find \(\int_{0}^{b}\vert 2x\vert \,dx\) for any real number \(b.\)

Question

If \(f\) is an odd function, show that \(\int_{-a}^{a}f(x)\,dx = 0\).

Question

Find the constant \(k\), where \(0\leq k\leq \,3\), for which \[ {\int_{0}^{3}{{\dfrac{{x}}{\sqrt{x^{2}+16}}}dx={\dfrac{{3k}}{\sqrt{k^{2}+16}}} }} \]

Question

If \(n\) is a positive integer, for what number is \[ \int_{0}^{a}x^{n-1} dx= \dfrac{1}{n} \]

Question

If \(f\) is a continuous function defined on the interval \([0,1]\), show that \[ {\int_{0}^{\pi }{x f(\sin x)\,dx={\dfrac{{\pi }}{{2}}}{\int_{0}^{\pi }{f(\sin x)\,dx}}}} \]

Question

Prove that \(\int \csc x\,dx=\ln \left\vert \csc x-\cot x\right\vert +C\). [Hint: Multiply and divide the integrand by \((\csc x-\cot x)\).]

Question

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.

Question

Find \(\int \sqrt[n]{{a\,{+}\,bx}}\,dx\), where \(a\) and \(b\) are real numbers, \(b\neq 0\), and \(n\geq 2\) is an integer.

Question

If \(f\) is continuous for all \(x\), which of the following integrals have the same value?

  1. \(\int_{a}^{b}{f(x)\,dx }\)
  2. \(\int_{0}^{b-a}{f(x+a)\,dx } \)
  3. \(\int_{a+c}^{b+c}{f(x+c)\,dx }\)

Challenge Problems

Question

Find \(\int {{\dfrac{{x^{6}+3x^{4}+3x^{2}+x+1}}{{(x^{2}+1)^{2}}}}}\,dx\).

Question

Find \(\int \dfrac{\sqrt[4]{x}}{\sqrt{x}+\sqrt[3]{x}}dx\).

Question

Find \(\int \dfrac{3x+2}{x\sqrt{x+1}}\ dx\).

Question

Find \(\int \dfrac{dx}{(x\ln x) [\ln (\ln x)] }\).

Question

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 \(ma=mg-kv\).)

Question

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.)

  1. \(\dfrac{y^{2}}{x}\dfrac{dy}{dx}=1+x^{2} \)
  2. \(\dfrac{dy}{dx}=y\dfrac{x^{2}-2x+1}{y+3}\)
  3. \(y\dfrac{dy}{dx}=\dfrac{x^{2}}{y+4}\);  if \(y=2\) when \(x=8\)