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chapter6.2r
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à 6.2ïGraphs of Polar Equations
äïPlease graph the following polar equations.
â
êêêëPlease see Details.
éSêêèIn order to draw a graph of r = 2∙cos Θ using a
@fig6201.bmp,15,25
êêê polar coordinate system, you should plot a suf-
êêê ficient number of ordered pairs to be able to
êêê visualize the graph then draw a smooth curve
êêê through the points.ïYou can choose any angle Θ,
êêê substitute it into the equation to find r, then
êêê plot the point on the coordinate system.ïThe
calculator can be used to evaluate the trigonometric functions of the
angle Θ.ïYou can also use the Key Feature in this program to generate
an adequate number of points to get a good graph.ïFor example, in the
Key Feature when Θ is 30°, the cos Θ is √3/2.ïThus, an ordered pair for
r = 2∙cos Θ is (30°, √3).ïUsing the table of values in the Key Feature,
we can generate the following list of points on the graph of r = 2∙cosΘ.
#ëΘ │ï0° │ 30° │ 45° │ 60° │ 90° │ 120° │ 135° │ 150° │ 180° │
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï2ï│ √3ï│ √2ï│ 1è│ 0è│ -1è│ï-√2 │ï-√3 │ï-2ï│
These points are shown in the figure and are used to produce a graph of
r = 2∙cos Θ.ïNotice that for this graph, angles from 180° to 360° just
retrace the circle and provide no additional points.ïThis will not al-
ways be the case for every polar equation.
1ë Draw a graph of the polar equation r = 1 - cos Θ.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6202.bmp,25,45
@fig6203.bmp,25,45
üïUse the Key Feature to generate the following table of points.
#ëΘ │ï0ï│ π/4 │ π/2 │ 3π/4│ïπï│ 5π/4 │ 3π/2 │ 7π/4 │ï2πï│
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï0ï│ .29 │ï1ï│ 1.7 │ï2ï│ 1.7ï│ï1è│ï.29 │è0ï│
êêêêïr = 1 - cos Θ
@fig6202.bmp,3100,2100
This curve is called a cardioid because of the heartlike shape.
Ç A
2ë Draw a graph of the polar equation r = 2∙(1 - sin Θ).
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6204.bmp,25,45
@fig6205.bmp,25,45
üïUse the Key Feature to generate the following table of points.
#ëΘ │ï0ï│ π/4 │ π/2 │ 3π/4│ïπï│ 5π/4 │ 3π/2 │ 7π/4 │ï2πï│
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï2ï│ .59 │ï0ï│ .59 │ï2ï│ 3.4ï│ï4è│ï3.4 │è2ï│
êêêêïr = 2∙(1 - sin Θ)
@fig6205.bmp,3100,2100
êêè This curve is also called a cardioid.
Ç B
3ë Draw a graph of the polar equation r = 2∙sin Θ.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6206.bmp,25,45
@fig6207.bmp,25,45
üïUse the Key Feature to generate the following table of points.
#ëΘ │ï0° │ 30° │ 45° │ 60° │ 90° │ 120° │ 135° │ 150° │ 180° │
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï0ï│ï1ï│ √2ï│ √3ï│ï2ï│ï√3ï│è√2 │è1ï│è0ï│
êêêêïr = 2∙sin Θ
@fig6207.bmp,3100,2100
This curve is also called a circle or rose curve with one petal.
Ç B
4ë Draw a graph of the polar equation Θ = π/6.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6208.bmp,25,45
@fig6209.bmp,25,35
üïTo draw a graph of Θ = π/6, you should note that r can assume
any value, but Θ must be π/6.
#ëΘ │ π/6 │ π/6 │ π/6 │ π/6 │ π/6 │ π/6ï│ π/6ï│ π/6ï│ π/6ï│
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï0ï│ï1ï│ï2ï│ï3ï│ï4ï│ï-1ï│è-2 │ï-3ï│ï-4ï│
êêêêïΘ = π/6
@fig6209.bmp,3100,2300
êëThis is a graph of a line through the origin.
Ç B
5ë Draw a graph of the polar equation r = 2.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6210.bmp,25,45
@fig6211.bmp,25,35
üïTo draw a graph of r = 2, you should note that Θ can assume
any value, but r must be 2.
#ëΘ │ï0ï│ π/6 │ π/3 │ π/4 │ π/2 │ 2π/3 │ 3π/4 │ 5π/6 │ïπè│
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï2ï│ï2ï│ï2ï│ï2ï│ï2ï│è2ï│è2ï│ï2è│ï2è│
êêêêïr = 2
@fig6210.bmp,3100,2300
êëThis curve is a circle centered at the origin.
Ç A
6ë Draw a graph of the polar equation r = 1 + 2∙cos Θ.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6212.bmp,25,35
@fig6213.bmp,25,45
üïUse the Key Feature to generate the following table of points.
#ëΘ │ï0ï│ π/4 │ π/2 │ 3π/4│ïπï│ 5π/4 │ 3π/2 │ 7π/4 │ï2πï│
#ë──│─────│─────│─────│─────│─────│──────│──────│──────│──────│
#ër │ï3ï│ 2.4 │ï1ï│-.41 │ -1ï│ -.41 │ï1è│ï2.4 │è3ï│
êêêêïr = 1 + 2∙cos Θ
@fig6212.bmp,3100,2100
êêThis curve is called a limacon with a loop.
Ç A
# 7ë Draw a graph of the polar equation rì = cos 2Θ.
ëA)êêê B)êêê C)èå
êêêêêêêêèof
êêêêêêêêïç
@fig6214.bmp,25,45
@fig6215.bmp,25,45
üïUse the Key Feature to generate the following table of points.
#êêïΘ │ï0ï│ π/6 │ π/4 │ 3π/4│ 5π/6│ïπï│
#êêï──│─────│─────│─────│─────│─────│─────│
#êêïr │ ±1ï│ ±.7 │ï0ï│ï0ï│ ±.7 │ ±1ï│
#êêêë rì = cos 2Θ
@fig6215.bmp,3100,2100
êêè This curve is called a lemniscate.
Ç B
8êè Draw a graph of r = cos 2Θ.
ëA)êêê B)êêê C)ïå
êêêêêêêêïof
êêêêêêêê ç
@fig6216.bmp,25,45
@fig6217.bmp,25,45
üêêêèr = cos 2Θ
@fig6216.bmp,3150,800
êèThis curve is called a rose curve with four petals.
Ç A