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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

how did you get 1640
Noor Reply
If auger is pair are the roots of equation x2+5x-3=0
Peter Reply
Wayne and Dennis like to ride the bike path from Riverside Park to the beach. Dennis’s speed is seven miles per hour faster than Wayne’s speed, so it takes Wayne 2 hours to ride to the beach while it takes Dennis 1.5 hours for the ride. Find the speed of both bikers.
MATTHEW Reply
420
Sharon
from theory: distance [miles] = speed [mph] × time [hours] info #1 speed_Dennis × 1.5 = speed_Wayne × 2 => speed_Wayne = 0.75 × speed_Dennis (i) info #2 speed_Dennis = speed_Wayne + 7 [mph] (ii) use (i) in (ii) => [...] speed_Dennis = 28 mph speed_Wayne = 21 mph
George
Let W be Wayne's speed in miles per hour and D be Dennis's speed in miles per hour. We know that W + 7 = D and W * 2 = D * 1.5. Substituting the first equation into the second: W * 2 = (W + 7) * 1.5 W * 2 = W * 1.5 + 7 * 1.5 0.5 * W = 7 * 1.5 W = 7 * 3 or 21 W is 21 D = W + 7 D = 21 + 7 D = 28
Salma
Devon is 32 32​​ years older than his son, Milan. The sum of both their ages is 54 54​. Using the variables d d​ and m m​ to represent the ages of Devon and Milan, respectively, write a system of equations to describe this situation. Enter the equations below, separated by a comma.
Aaron Reply
find product (-6m+6) ( 3m²+4m-3)
SIMRAN Reply
-42m²+60m-18
Salma
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bill
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bill
-24m+3+3mÁ^2
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Bajemah
-6m(3mA²+4m-3)+6(3mA²+4m-3) =-18m²A²-24m²+18m+18mA²+24m-18 Rearrange like items -18m²A²-24m²+42m+18A²-18
Salma
complete the table of valuesfor each given equatio then graph. 1.x+2y=3
Jovelyn Reply
x=3-2y
Salma
y=x+3/2
Salma
Hi
Enock
given that (7x-5):(2+4x)=8:7find the value of x
Nandala
3x-12y=18
Kelvin
please why isn't that the 0is in ten thousand place
Grace Reply
please why is it that the 0is in the place of ten thousand
Grace
Send the example to me here and let me see
Stephen
A meditation garden is in the shape of a right triangle, with one leg 7 feet. The length of the hypotenuse is one more than the length of one of the other legs. Find the lengths of the hypotenuse and the other leg
Marry Reply
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state in which quadrant or on which axis each of the following angles given measure. in standard position would lie 89°
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Method
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Enock
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Roger
The Jones family took a 15 mile canoe ride down the Indian River in three hours. After lunch, the return trip back up the river took five hours. Find the rate, in mph, of the canoe in still water and the rate of the current.
cameron Reply
Shakir works at a computer store. His weekly pay will be either a fixed amount, $925, or $500 plus 12% of his total sales. How much should his total sales be for his variable pay option to exceed the fixed amount of $925.
mahnoor Reply
I'm guessing, but it's somewhere around $4335.00 I think
Lewis
12% of sales will need to exceed 925 - 500, or 425 to exceed fixed amount option. What amount of sales does that equal? 425 ÷ (12÷100) = 3541.67. So the answer is sales greater than 3541.67. Check: Sales = 3542 Commission 12%=425.04 Pay = 500 + 425.04 = 925.04. 925.04 > 925.00
Munster
difference between rational and irrational numbers
Arundhati Reply
When traveling to Great Britain, Bethany exchanged $602 US dollars into £515 British pounds. How many pounds did she receive for each US dollar?
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Jazmine trained for 3 hours on Saturday. She ran 8 miles and then biked 24 miles. Her biking speed is 4 mph faster than her running speed. What is her running speed?
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d=r×t the equation would be 8/r+24/r+4=3 worked out
Sheirtina
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Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
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