<< Chapter < Page Chapter >> Page >

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

Graphical

For the following exercises, test the equation for symmetry.

r = 3 3 cos θ

symmetric with respect to the polar axis

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

r = 5 sin 2 θ

symmetric with respect to the pole

Got questions? Get instant answers now!

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

r = 2 2 cos θ

cardioid
Graph of given cardioid.

Got questions? Get instant answers now!

r = 3 + 3 sin θ

cardioid
Graph of given cardioid.

Got questions? Get instant answers now!

r = 7 + 4 sin θ

one-loop/dimpled limaçon

Graph of given one-loop/dimpled limaçon
Got questions? Get instant answers now!

r = 5 + 4 cos θ

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

Got questions? Get instant answers now!

r = 1 + 3 sin θ

inner loop/two-loop limaçon

Graph of given inner loop/two-loop limaçon
Got questions? Get instant answers now!

r = 5 + 7 sin θ

inner loop/two-loop limaçon

Graph of given inner loop/two-loop limaçon
Got questions? Get instant answers now!

r = 5 + 6 cos θ

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

Got questions? Get instant answers now!

r 2 = 10 cos ( 2 θ )

lemniscate

Graph of given lemniscate (along horizontal axis)
Got questions? Get instant answers now!

r 2 = 10 sin ( 2 θ )

lemniscate

Graph of given lemniscate (along y=x)
Got questions? Get instant answers now!

r = 3 cos ( 2 θ )

rose curve

Graph of given rose curve - four petals.
Got questions? Get instant answers now!

r = 4 sin ( 4 θ )

rose curve

Graph of given rose curve - eight petals.
Got questions? Get instant answers now!

r = θ

Archimedes’ spiral

Graph of given Archimedes' spiral
Got questions? Get instant answers now!

r = 3 θ

Archimedes’ spiral

Graph of given Archimedes' spiral
Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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)
Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

r = sin θ + θ , r = sin θ θ

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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
Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

r 1 = 6 4 cos θ , r 2 = 4

( 4 , π 3 ) , ( 4 , 5 π 3 )

Got questions? Get instant answers now!

r 1 = 1 + sin θ , r 2 = 3 sin θ

Got questions? Get instant answers now!

r 1 = 1 + cos θ , r 2 = 3 cos θ

( 3 2 , π 3 ) , ( 3 2 , 5 π 3 )

Got questions? Get instant answers now!

r 1 = cos ( 2 θ ) , r 2 = sin ( 2 θ )

Got questions? Get instant answers now!

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

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

Got questions? Get instant answers now!

r 1 = 3 , r 2 = 2 sin ( θ )

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

r 1 = 1 + cos θ , r 2 = 1 sin θ

Got questions? Get instant answers now!

Questions & Answers

Discuss the differences between taste and flavor, including how other sensory inputs contribute to our  perception of flavor.
John Reply
taste refers to your understanding of the flavor . while flavor one The other hand is refers to sort of just a blend things.
Faith
While taste primarily relies on our taste buds, flavor involves a complex interplay between taste and aroma
Kamara
which drugs can we use for ulcers
Ummi Reply
omeprazole
Kamara
what
Renee
what is this
Renee
is a drug
Kamara
of anti-ulcer
Kamara
Omeprazole Cimetidine / Tagament For the complicated once ulcer - kit
Patrick
what is the function of lymphatic system
Nency Reply
Not really sure
Eli
to drain extracellular fluid all over the body.
asegid
The lymphatic system plays several crucial roles in the human body, functioning as a key component of the immune system and contributing to the maintenance of fluid balance. Its main functions include: 1. Immune Response: The lymphatic system produces and transports lymphocytes, which are a type of
asegid
to transport fluids fats proteins and lymphocytes to the blood stream as lymph
Adama
what is anatomy
Oyindarmola Reply
Anatomy is the identification and description of the structures of living things
Kamara
what's the difference between anatomy and physiology
Oyerinde Reply
Anatomy is the study of the structure of the body, while physiology is the study of the function of the body. Anatomy looks at the body's organs and systems, while physiology looks at how those organs and systems work together to keep the body functioning.
AI-Robot
what is enzymes all about?
Mohammed Reply
Enzymes are proteins that help speed up chemical reactions in our bodies. Enzymes are essential for digestion, liver function and much more. Too much or too little of a certain enzyme can cause health problems
Kamara
yes
Prince
how does the stomach protect itself from the damaging effects of HCl
Wulku Reply
little girl okay how does the stomach protect itself from the damaging effect of HCL
Wulku
it is because of the enzyme that the stomach produce that help the stomach from the damaging effect of HCL
Kamara
function of digestive system
Ali Reply
function of digestive
Ali
the diagram of the lungs
Adaeze Reply
what is the normal body temperature
Diya Reply
37 degrees selcius
Xolo
37°c
Stephanie
please why 37 degree selcius normal temperature
Mark
36.5
Simon
37°c
Iyogho
the normal temperature is 37°c or 98.6 °Fahrenheit is important for maintaining the homeostasis in the body the body regular this temperature through the process called thermoregulation which involves brain skin muscle and other organ working together to maintain stable internal temperature
Stephanie
37A c
Wulku
what is anaemia
Diya Reply
anaemia is the decrease in RBC count hemoglobin count and PVC count
Eniola
what is the pH of the vagina
Diya Reply
how does Lysin attack pathogens
Diya
acid
Mary
I information on anatomy position and digestive system and there enzyme
Elisha Reply
anatomy of the female external genitalia
Muhammad Reply
Organ Systems Of The Human Body (Continued) Organ Systems Of The Human Body (Continued)
Theophilus Reply
what's lochia albra
Kizito
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 9

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Precalculus' conversation and receive update notifications?

Ask