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Sketch the graph of r = θ over the interval [ 0 , 4 π ] .

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Summary of curves

We have explored a number of seemingly complex polar curves in this section. [link] and [link] summarize the graphs and equations for each of these curves.

Four graphs side by side - a summary. (A) is a circle: r=asin(theta) or r=acos(theta). (B) is a cardioid: r= a + or - bcos(theta), or r = a + or - b sin(theta). a>0, b>0, a/b=1. (C) is one-loop limaçons. r= a + or - bcos(theta), or r= a + or - bsin(theta). a>0, b>0, 1<a/b<2. (D) is inner-loop limaçons. R = a + or - bcos(theta), or r = a + or - bsin(theta). A>0, b>0, a<b.
Four graphs side by side - a summary. (A) is lemniscates. R^2 = a^2cos(2theta), or r^2=a^2sin(2theta). a is not equal to 0. (B) is a rsose curve (n even). R = acos(ntheta), or r=asin(ntheta). N is even, and there are 2n petals. (C) is a rose curve (n odd). R = acos(ntheta), or r=asin(theta). N is odd, and there are n petals. (D) is an Archimedes's spiral. R=theta, and theta >=0.

Access these online resources for additional instruction and practice with graphs of polar coordinates.

Key concepts

  • It is easier to graph polar equations if we can test the equations for symmetry with respect to the line θ = π 2 , the polar axis, or the pole.
  • There are three symmetry tests that indicate whether the graph of a polar equation will exhibit symmetry. If an equation fails a symmetry test, the graph may or may not exhibit symmetry. See [link] .
  • Polar equations may be graphed by making a table of values for θ and r .
  • The maximum value of a polar equation is found by substituting the value θ that leads to the maximum value of the trigonometric expression.
  • The zeros of a polar equation are found by setting r = 0 and solving for θ . See [link] .
  • Some formulas that produce the graph of a circle in polar coordinates are given by r = a cos θ and r = a sin θ . See [link] .
  • The formulas that produce the graphs of a cardioid are given by r = a ± b cos θ and r = a ± b sin θ , for a > 0 , b > 0 , and a b = 1. See [link] .
  • The formulas that produce the graphs of a one-loop limaçon are given by r = a ± b cos θ and r = a ± b sin θ for 1 < a b < 2. See [link] .
  • The formulas that produce the graphs of an inner-loop limaçon are given by r = a ± b cos θ and r = a ± b sin θ for a > 0 , b > 0 , and a < b . See [link] .
  • The formulas that produce the graphs of a lemniscates are given by r 2 = a 2 cos 2 θ and r 2 = a 2 sin 2 θ , where a 0. See [link] .
  • The formulas that produce the graphs of rose curves are given by r = a cos n θ and r = a sin n θ , where a 0 ; if n is even, there are 2 n petals, and if n is odd, there are n petals. See [link] and [link] .
  • The formula that produces the graph of an Archimedes’ spiral is given by r = θ , θ 0. See [link] .

Section exercises

Verbal

Describe the three types of symmetry in polar graphs, and compare them to the symmetry of the Cartesian plane.

Symmetry with respect to the polar axis is similar to symmetry about the x -axis, symmetry with respect to the pole is similar to symmetry about the origin, and symmetric with respect to the line θ = π 2 is similar to symmetry about the y -axis.

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Which of the three types of symmetries for polar graphs correspond to the symmetries with respect to the x -axis, y -axis, and origin?

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What are the steps to follow when graphing polar equations?

Test for symmetry; find zeros, intercepts, and maxima; make a table of values. Decide the general type of graph, cardioid, limaçon, lemniscate, etc., then plot points at θ = 0 , π 2 , π and  3 π 2 , and sketch the graph.

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Describe the shapes of the graphs of cardioids, limaçons, and lemniscates.

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What part of the equation determines the shape of the graph of a polar equation?

The shape of the polar graph is determined by whether or not it includes a sine, a cosine, and constants in the equation.

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Graphical

For the following exercises, test the equation for symmetry.

r = 3 3 cos θ

symmetric with respect to the polar axis

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r = 3 sin 2 θ

symmetric with respect to the polar axis, symmetric with respect to the line θ = π 2 , symmetric with respect to the pole

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r = 5 sin 2 θ

symmetric with respect to the pole

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For the following exercises, graph the polar equation. Identify the name of the shape.

r = 2 2 cos θ

cardioid
Graph of given cardioid.

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r = 3 + 3 sin θ

cardioid
Graph of given cardioid.

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r = 7 + 4 sin θ

one-loop/dimpled limaçon

Graph of given one-loop/dimpled limaçon
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r = 5 + 4 cos θ

one-loop/dimpled limaçon
Graph of given one-loop/dimpled limaçon

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r = 1 + 3 sin θ

inner loop/two-loop limaçon

Graph of given inner loop/two-loop limaçon
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r = 5 + 7 sin θ

inner loop/two-loop limaçon

Graph of given inner loop/two-loop limaçon
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r = 5 + 6 cos θ

inner loop/two-loop limaçon
Graph of given inner loop/two-loop limaçon

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r 2 = 10 cos ( 2 θ )

lemniscate

Graph of given lemniscate (along horizontal axis)
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r 2 = 10 sin ( 2 θ )

lemniscate

Graph of given lemniscate (along y=x)
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r = 3 cos ( 2 θ )

rose curve

Graph of given rose curve - four petals.
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r = 4 sin ( 4 θ )

rose curve

Graph of given rose curve - eight petals.
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r = θ

Archimedes’ spiral

Graph of given Archimedes' spiral
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r = 3 θ

Archimedes’ spiral

Graph of given Archimedes' spiral
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Technology

For the following exercises, use a graphing calculator to sketch the graph of the polar equation.

r = 2 sin θ tan θ , a cissoid

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r = 2 1 sin 2 θ , a hippopede

Graph of given hippopede (two circles that are centered along the x-axis and meet at the origin)
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For the following exercises, use a graphing utility to graph each pair of polar equations on a domain of [ 0 , 4 π ] and then explain the differences shown in the graphs.

r = θ , r = θ + sin θ

They are both spirals, but not quite the same.

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r = sin θ + θ , r = sin θ θ

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r = 2 sin ( θ 2 ) , r = θ sin ( θ 2 )

Both graphs are curves with 2 loops. The equation with a coefficient of θ has two loops on the left, the equation with a coefficient of 2 has two loops side by side. Graph these from 0 to 4 π to get a better picture.

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r = sin ( cos ( 3 θ ) ) r = sin ( 3 θ )

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On a graphing utility, graph r = sin ( 16 5 θ ) on [ 0 , 4 π ] , [ 0 , 8 π ] , [ 0 , 12 π ] , and [ 0 , 16 π ] . Describe the effect of increasing the width of the domain.

When the width of the domain is increased, more petals of the flower are visible.

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On a graphing utility, graph and sketch r = sin θ + ( sin ( 5 2 θ ) ) 3 on [ 0 , 4 π ] .

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On a graphing utility, graph each polar equation. Explain the similarities and differences you observe in the graphs.

r 1 = 3 sin ( 3 θ ) r 2 = 2 sin ( 3 θ ) r 3 = sin ( 3 θ )

The graphs are three-petal, rose curves. The larger the coefficient, the greater the curve’s distance from the pole.

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On a graphing utility, graph each polar equation. Explain the similarities and differences you observe in the graphs.

r 1 = 3 + 3 cos θ r 2 = 2 + 2 cos θ r 3 = 1 + cos θ
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On a graphing utility, graph each polar equation. Explain the similarities and differences you observe in the graphs.

r 1 = 3 θ r 2 = 2 θ r 3 = θ

The graphs are spirals. The smaller the coefficient, the tighter the spiral.

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Extensions

For the following exercises, draw each polar equation on the same set of polar axes, and find the points of intersection.

r 1 = 3 + 2 sin θ , r 2 = 2

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r 1 = 6 4 cos θ , r 2 = 4

( 4 , π 3 ) , ( 4 , 5 π 3 )

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r 1 = 1 + sin θ , r 2 = 3 sin θ

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r 1 = 1 + cos θ , r 2 = 3 cos θ

( 3 2 , π 3 ) , ( 3 2 , 5 π 3 )

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r 1 = cos ( 2 θ ) , r 2 = sin ( 2 θ )

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r 1 = sin 2 ( 2 θ ) , r 2 = 1 cos ( 4 θ )

( 0 , π 2 ) , ( 0 , π ) , ( 0 , 3 π 2 ) , ( 0 , 2 π )

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r 1 = 3 , r 2 = 2 sin ( θ )

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r 1 2 = sin θ , r 2 2 = cos θ

( 8 4 2 , π 4 ) , ( 8 4 2 , 5 π 4 ) and at θ = 3 π 4 , 7 π 4 since r is squared

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r 1 = 1 + cos θ , r 2 = 1 sin θ

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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
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what is field
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physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
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what is ogarnic chemistry
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determine the slope giving that 3y+ 2x-14=0
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Another formula for Acceleration
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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?
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Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
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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
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Source:  OpenStax, Algebra and trigonometry. OpenStax CNX. Nov 14, 2016 Download for free at https://legacy.cnx.org/content/col11758/1.6
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