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Let’s revisit the checkpoint associated with [link] , only this time, let’s integrate with respect to y . Let be the region depicted in the following figure. Find the area of R by integrating with respect to y .

This figure is has two graphs in the first quadrant. They are the functions f(x) = squareroot of x and g(x)= 3/2 – x/2. In between these graphs is a shaded region, bounded to the left by f(x) and to the right by g(x). All of which is above the x-axis. The shaded area is between x=0 and x=3.

5 3 units 2

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Key concepts

  • Just as definite integrals can be used to find the area under a curve, they can also be used to find the area between two curves.
  • To find the area between two curves defined by functions, integrate the difference of the functions.
  • If the graphs of the functions cross, or if the region is complex, use the absolute value of the difference of the functions. In this case, it may be necessary to evaluate two or more integrals and add the results to find the area of the region.
  • Sometimes it can be easier to integrate with respect to y to find the area. The principles are the same regardless of which variable is used as the variable of integration.

Key equations

  • Area between two curves, integrating on the x -axis
    A = a b [ f ( x ) g ( x ) ] d x
  • Area between two curves, integrating on the y -axis
    A = c d [ u ( y ) v ( y ) ] d y

For the following exercises, determine the area of the region between the two curves in the given figure by integrating over the x -axis .

y = x 2 3 and y = 1

This figure is has two graphs. They are the functions f(x) = x^2-3and g(x)=1. In between these graphs is a shaded region, bounded above by g(x) and below by f(x). The shaded area is between x=-2 and x=2.

32 3

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For the following exercises, split the region between the two curves into two smaller regions, then determine the area by integrating over the x -axis . Note that you will have two integrals to solve.

y = x 3 and y = x 2 + x

This figure is has two graphs. They are the functions f(x) = x^3 and g(x)= x^2+x. These graphs intersect twice. The regions between the intersections are shaded. The first region is bounded above by f(x) and below by g(x). The second region is bounded above by g(x) and below by f(x).

13 12

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y = cos θ and y = 0.5 , for 0 θ π

This figure is has two graphs. They are the functions f(theta) = cos(theta) and g(x)= 0.5. These graphs intersect twice. The regions between the intersections are shaded. The first region is bounded above by f(x) and below by g(x). The second region is bounded above by g(x) and below by f(x).
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For the following exercises, determine the area of the region between the two curves by integrating over the y -axis .

For the following exercises, graph the equations and shade the area of the region between the curves. Determine its area by integrating over the x -axis .

y = x 2 and y = x 2 + 18 x


This figure is has two graphs. They are the functions f(x)=x^2 and g(x)=-x^2+18x. The region between the graphs is shaded, bounded above by g(x) and below by f(x). It is in the first quadrant.
243 square units

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y = 1 x , y = 1 x 2 , and x = 3

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y = cos x and y = cos 2 x on x = [ π , π ]


This figure is has two graphs. They are the functions y=cos(x) and y=cos^2(x). The graphs are periodic and resemble waves. There are four regions created by intersections of the curves. The areas are shaded.
4

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y = e x , y = e 2 x 1 , and x = 0

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y = e x , y = e x , x = −1 and x = 1


This figure is has two graphs. They are the functions f(x)=e^x and g(x)=e^-x. There are two shaded regions. In the second quadrant the region is bounded by x=-1, g(x) above and f(x) below. The second region is in the first quadrant and is bounded by f(x) above, g(x) below, and x=1.
2 ( e 1 ) 2 e

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y = e , y = e x , and y = e x

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y = | x | and y = x 2


This figure is has two graphs. They are the functions f(x)=x^2 and g(x)=absolute value of x. There are two shaded regions. The first region is in the second quadrant and is between g(x) above and f(x) below. The second region is in the first quadrant and is bounded above by g(x) and below by f(x).
1 3

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For the following exercises, graph the equations and shade the area of the region between the curves. If necessary, break the region into sub-regions to determine its entire area.

y = sin ( π x ) , y = 2 x , and x > 0

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y = 12 x , y = x , and y = 1


This figure is has three graphs. They are the functions f(x)=squareroot of x, y=12-x, and y=1. The region between the graphs is shaded, bounded above and to the left by f(x), above and to the right by the line y=12-x, and below by the line y=1. It is in the first quadrant.
34 3

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y = sin x and y = cos x over x = [ π , π ]

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y = x 3 and y = x 2 2 x over x = [ −1 , 1 ]


This figure is has two graphs. They are the functions f(x)=x^3 and g(x)=x^2-2x. There are two shaded regions between the graphs. The first region is bounded to the left by the line x=-2, above by g(x) and below by f(x). The second region is bounded above by f(x), below by g(x) and to the right by the line x=2.
5 2

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y = x 2 + 9 and y = 10 + 2 x over x = [ −1 , 3 ]

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y = x 3 + 3 x and y = 4 x


This figure is has two graphs. They are the functions f(x)=x^3+3x and g(x)=4x. There are two shaded regions between the graphs. The first region is bounded above by f(x) and below by g(x). The second region is bounded above by g(x), below by f(x).
1 2

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For the following exercises, graph the equations and shade the area of the region between the curves. Determine its area by integrating over the y -axis .

x = y 3 and x = 3 y 2

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x = 2 y and x = y 3 y


This figure is has two graphs. They are the equations x=2y and x=y^3-y. The graphs intersect in the third quadrant and again in the first quadrant forming two closed regions in between them.
9 2

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x = −3 + y 2 and x = y y 2

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y 2 = x and x = y + 2


This figure is has two graphs. They are the equations x=y+2 and y^2=x. The graphs intersect, forming a region in between them
9 2

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x = | y | and 2 x = y 2 + 2

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x = sin y , x = cos ( 2 y ) , y = π / 2 , and y = π / 2


This figure is has two graphs. They are the equations x=cos(y) and x=sin(y). The graphs intersect, forming two regions bounded above by the line y=pi/2 and below by the line y=-pi/2.
3 3 2

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For the following exercises, graph the equations and shade the area of the region between the curves. Determine its area by integrating over the x -axis or y -axis, whichever seems more convenient.

y = x e x , y = e x , x = 0 , and x = 1


This figure is has two graphs. They are the equations y=xe^x and y=e^x. The graphs intersect, forming a region in between them in the first quadrant.
e −2

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x = y 3 + 2 y 2 + 1 and x = y 2 + 1


This figure is has two graphs. They are the equations x=-y^2+1 and x=y^3+2y^2. The graphs intersect, forming two regions in between them.
27 4

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y = | x | and y = x 2 1

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y = 4 3 x and y = 1 x


This figure is has two graphs. They are the equations y=4-3x and y=1/x. The graphs intersect, having region between them shaded. The region is in the first quadrant.
4 3 ln ( 3 )

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y = sin x , x = π / 6 , x = π / 6 , and y = cos 3 x

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y = x 2 3 x + 2 and y = x 3 2 x 2 x + 2


This figure is has two graphs. They are the equations y=x^2-3x+2 and y=x^3-2x^2-x+2. The graphs intersect, having region between them shaded.
1 2

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y = 2 cos 3 ( 3 x ) , y = −1 , x = π 4 , and x = π 4

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y + y 3 = x and 2 y = x


This figure is has two graphs. They are the equations 2y=x and y+y^3=x. The graphs intersect, forming two regions. The regions are shaded.
1 2

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y = 1 x 2 and y = x 2 1

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y = cos −1 x , y = sin −1 x , x = −1 , and x = 1


This figure is has two graphs. They are the equations y=arccos(x) and y=arcsin (x). The graphs intersect, forming two regions. The first region is bounded to the left by x=-1. The second region is bounded to the right by x=1. Both regions are shaded.
−2 ( 2 π )

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For the following exercises, find the exact area of the region bounded by the given equations if possible. If you are unable to determine the intersection points analytically, use a calculator to approximate the intersection points with three decimal places and determine the approximate area of the region.

[T] x = e y and y = x 2

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[T] y = x 2 and y = 1 x 2

1.067

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[T] y = 3 x 2 + 8 x + 9 and 3 y = x + 24

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[T] x = 4 y 2 and y 2 = 1 + x 2

0.852

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[T] x 2 = y 3 and x = 3 y

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[T] y = sin 3 x + 2 , y = tan x , x = −1.5 , and x = 1.5

7.523

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[T] y = 1 x 2 and y 2 = x 2

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[T] y = 1 x 2 and y = x 2 + 2 x + 1

3 π 4 12

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[T] x = 4 y 2 and x = 1 + 3 y + y 2

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[T] y = cos x , y = e x , x = π , and x = 0

1.429

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The largest triangle with a base on the x -axis that fits inside the upper half of the unit circle y 2 + x 2 = 1 is given by y = 1 + x and y = 1 x . See the following figure. What is the area inside the semicircle but outside the triangle?

This figure is has the graph of a circle with center at the origin and radius of 1. There is a triangle inscribed with base on the x-axis from -1 to 1 and the third corner at the point y=1.
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A factory selling cell phones has a marginal cost function C ( x ) = 0.01 x 2 3 x + 229 , where x represents the number of cell phones, and a marginal revenue function given by R ( x ) = 429 2 x . Find the area between the graphs of these curves and x = 0 . What does this area represent?

$ 33,333.33 total profit for 200 cell phones sold

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An amusement park has a marginal cost function C ( x ) = 1000 e x + 5 , where x represents the number of tickets sold, and a marginal revenue function given by R ( x ) = 60 0.1 x . Find the total profit generated when selling 550 tickets. Use a calculator to determine intersection points, if necessary, to two decimal places.

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The tortoise versus the hare: The speed of the hare is given by the sinusoidal function H ( t ) = 1 cos ( ( π t ) / 2 ) whereas the speed of the tortoise is T ( t ) = ( 1 / 2 ) tan −1 ( t / 4 ) , where t is time measured in hours and the speed is measured in miles per hour. Find the area between the curves from time t = 0 to the first time after one hour when the tortoise and hare are traveling at the same speed. What does it represent? Use a calculator to determine the intersection points, if necessary, accurate to three decimal places.

3.263 mi represents how far ahead the hare is from the tortoise

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The tortoise versus the hare: The speed of the hare is given by the sinusoidal function H ( t ) = ( 1 / 2 ) ( 1 / 2 ) cos ( 2 π t ) whereas the speed of the tortoise is T ( t ) = t , where t is time measured in hours and speed is measured in kilometers per hour. If the race is over in 1 hour, who won the race and by how much? Use a calculator to determine the intersection points, if necessary, accurate to three decimal places.

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For the following exercises, find the area between the curves by integrating with respect to x and then with respect to y . Is one method easier than the other? Do you obtain the same answer?

y = x 2 + 2 x + 1 and y = x 2 3 x + 4

343 24

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x = y 2 2 and x = 2 y

4 3

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For the following exercises, solve using calculus, then check your answer with geometry.

Determine the equations for the sides of the square that touches the unit circle on all four sides, as seen in the following figure. Find the area between the perimeter of this square and the unit circle. Is there another way to solve this without using calculus?

This figure is the graph of a circle centered at the origin with radius of 1. There is a circumscribed square around the circle.
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Find the area between the perimeter of the unit circle and the triangle created from y = 2 x + 1 , y = 1 2 x and y = 3 5 , as seen in the following figure. Is there a way to solve this without using calculus?

This figure is the graph of a circle centered at the origin with radius of 1. There are three lines intersecting the circle. The lines intersect the circle at three points to form a triangle within the circle.

π 32 25

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Questions & Answers

Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
Kate Reply
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Kate Reply
what is the change in momentum of a body?
Eunice Reply
what is a capacitor?
Raymond Reply
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
Maria Reply
please solve
Sharon
8m/s²
Aishat
What is Thermodynamics
Muordit
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
Saheed Reply
50 m/s due south east
Someone
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
Ramon Reply
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
Someone
definitely of physics
Haryormhidey Reply
how many start and codon
Esrael Reply
what is field
Felix Reply
physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
Collete
what is ogarnic chemistry
WISDOM Reply
determine the slope giving that 3y+ 2x-14=0
WISDOM
Another formula for Acceleration
Belty Reply
a=v/t. a=f/m a
IHUMA
innocent
Adah
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
Nassze Reply
how do lnternal energy measures
Esrael
Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
JALLAH Reply
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you. Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
What is specific heat capacity
Destiny Reply
Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius (or Kelvin). It is measured in Joules per kilogram per degree Celsius (J/kg°C).
AI-Robot
specific heat capacity is the amount of energy needed to raise the temperature of a substance by one degree Celsius or kelvin
ROKEEB
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Source:  OpenStax, Calculus volume 1. OpenStax CNX. Feb 05, 2016 Download for free at http://cnx.org/content/col11964/1.2
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