9.2 Graphs of Polar Eqs

Identify and graph the equation: r 4cos

r r2 4 cos

x y x2 2 4

x x y2 24 0

x x y2 24 4 4

x y 2 42 2

0

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30

4560

7590105120

135

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255 270 285300

315

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34543210

r a2 cos Circle: radius a; center at (a, 0) in rectangular coordinates.

r a 2 cos Circle: radius a; center at (-a, 0) in rectangular coordinates.

r a2 sin Circle: radius a; center at (0, a) in rectangular coordinates.

r a 2 sin Circle: radius a; center at (0, -a) in rectangular coordinates.

4

2

2

5 5

sin4r

sin6r2

2

4

6

8

5 5

In order to use your graphing calculator to graph Polar Equations, change your MODE to POLAR (instead of Function). Also, change your viewing window as follows…

For DEGREES:

qmin = 0qmax = 360qstep = 10Xmin = -8Xmax = 8Xscl = 1Ymin = -8Ymax = 8Yscl = 1

For RADIANS:

qmin = 0qmax = 2 qstep = /18Xmin = -8Xmax = 8Xscl = 1Ymin = -8Ymax = 8Yscl = 1

Now that you have your graphing calculator set up to graph Polar Equations, graph the following equations and see if you can identify the shape and how the numbers affect the graph itself…

r = 2 + 2sin r = 2 + 2cosr = 1 + sinr = -2 + -2cosr = 3 + 3sinr = 3 + 3cos

cosaar

Is the graph of a CARDIOID (heart) shape, symmetric to either the x axis (for cosine) or y axis (for sine)

sinaar or

6

4

2

2

4

6

5 5 10

6

4

2

2

4

6

5 5 10

Now graph the following equations and see if you can identify the shape and how the numbers affect the graph itself…

r = 2 + 3sin r = 1 + 2cosr = 1 + 4sinr = 3 + 2cosr = 2 + sinr = 4 + 2cos

cosbar

Is the graph of a Limacon (pronounced “lee-ma-sahn”) shape, symmetric to either the x axis (for cosine) or y axis (for sine)

sinbar or

2

1

1

2

3

4 2 2 4

6

4

2

2

4

6

5 5

cos42 r

Notice how the graph of a limacon changes depending on whether a > b or a < b

sin23r

2

1

1

2

3

4 2 2 4

6

4

2

2

4

6

5 5

a < ba > b

Now graph the following equations and see if you can identify the shape and how the numbers affect the graph itself…

r = 3sin2 r = 2cos4r = 4sin3r = 5cos2r = 3sinr = -3cos3

bar cos

Is the graph of a ROSE shape, symmetric to either the x axis (for cosine) or y axis (for sine)

bar sinor

3

2

1

1

2

3

4 2 2 4

4

3

2

1

1

2

3

4

6 4 2 2 4 6

2cos3r

Notice how the ‘b’ value affects the graph: if b is even, then there are ‘2*b’ number of rose petals (loops); if ‘b’ is odd, there are ‘b’ number of petals

3sin4rand

3

2

1

1

2

3

4 2 2 4

4

3

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1

1

2

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4

6 4 2 2 4 6

Below are the graphs of the roses for

The next type of graph we are going to look at involves the following formats for the equation:

and

2cos2 ar 2sin2 ar

However, with the graphing calculator, we cannotType the equations in this fashion.Instead, we take the square root of both sides of the Equation and type that equation into the calculator.For example:

is typed in as2cos92 r 2cos9r

Now graph the following equations and see if you can identify the shape and how the numbers affect the graph itself…

2cos92 r

2sin42 r

2cos162 r

2sin52 r

Is the graph of a lemniscate (pronounced “lem-nah-scut”) shape, symmetric to either the x axis (for cosine) or the line y = x (for sine)

or2cos2 ar 2sin2 ar 4

3

2

1

1

2

3

4

6 4 2 2 4 6

4

3

2

1

1

2

3

4

6 4 2 2 4 6

The next type of graph we are going to look at involves the following format for the equation:

ar

However, with the graphing calculator, we will not beable to see much of the graph if we work with degrees,because r keeps increasing as the angle measure does.So switch to RADIAN MODE and be sure to modifythe X and Y values in WINDOW to accommodate each graph.

Now graph the following equations and see if you can identify the shape and how the numbers affect the graph itself…

r

3r

2r

Is the graph of a Spiral of Archimedes (pronounced “Ar-cah-mee-dees”) shape.

ar 12

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