Symmetry in Graphs of Polar Equations On to Sec. 6.5a!!!
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Transcript of Symmetry in Graphs of Polar Equations On to Sec. 6.5a!!!
Symmetry in Graphs Symmetry in Graphs of Polar Equationsof Polar Equations
On to Sec. 6.5a!!!On to Sec. 6.5a!!!
Recall our three types of symmetry…
θ
,θr
θ
1. The x-axis (polar axis) as a line of symmetry
x
y
, θ , π θr r
Recall our three types of symmetry…
π θ ,θr
θ
2. The y-axis (the line ) as a line of symmetry
x
y , π θ , θr r
θ π 2
Recall our three types of symmetry…
θ π
,θr
θ
3. The origin (the pole) as a point of symmetry
x
y
,θ ,θ πr r
Symmetry Tests for Polar Graphs
,θr
,θr
,θ or ,θ πr r
The graph of a polar equation has the indicated symmetry ifeither replacement produces an equivalent polar equation.
To Test for Symmetry Replace By
1. about the x-axis
2. about the y-axis
3. about the origin
,θr , θ or , π θr r
, θ or , π θr r
Guided PracticeUse symmetry tests to determine if the graph if symmetricabout the x-axis, y-axis, or origin. Confirm your answersgraphically.
4sin3θr
Symmetric about the Symmetric about the yy-axis-axis
(check the graph first???)
Guided PracticeUse symmetry tests to determine if the graph if symmetricabout the x-axis, y-axis, or origin. Confirm your answersgraphically.
1 2cosr Symmetric about the Symmetric about the xx-axis-axis
Guided PracticeUse symmetry tests to determine if the graph if symmetricabout the x-axis, y-axis, or origin. Confirm your answersgraphically.
1 3sinr Symmetric about the Symmetric about the yy-axis-axis
Guided PracticeUse symmetry tests to determine if the graph if symmetricabout the x-axis, y-axis, or origin. Confirm your answersgraphically.
7sin3r Symmetric about the Symmetric about the yy-axis-axis
Guided PracticeUse symmetry tests to determine if the graph if symmetricabout the x-axis, y-axis, or origin. Confirm your answersgraphically. 2
1 cosr
Symmetric about the Symmetric about the xx-axis-axis
We can “analyze” the graphs of polar equations in much thesame way as we have for rectangular equations…
As before, we check:
DomainDomain RangeRange SymmetrySymmetry
ContinuityContinuity BoundednessBoundedness
AsymptotesAsymptotes
Maximum r-valueMaximum r-value (this is the new one…)
Let’s focus on that last one for a bit…
Find the maximum r-value of 2 2cosθr
Maximum r-value = 4Maximum r-value = 4
Check algebraically and graphically…
Let’s focus on that last one for a bit…
Identify the points on the graph offor that give maximum r-values0 θ 2π
3cos 2θr
3,03π
3,2
3, ππ
3,2
Guided PracticeGuided PracticeAnalyze the graph of the given polar curve.
Domain:Domain:
8r , Range:Range: 8r
Symmetry:Symmetry: About the x-axis, y-axis, and origin
Continuity:Continuity: Continuous
Boundedness:Boundedness: Bounded
Asymptotes:Asymptotes: None
Maximum Maximum rr-value:-value: 8
The graph???
Guided PracticeGuided PracticeAnalyze the graph of the given polar curve.
Domain:Domain:
6 6 Range:Range: ,
Symmetry:Symmetry: About the origin
Continuity:Continuity: Continuous
Boundedness:Boundedness: Unbounded
Asymptotes:Asymptotes: None
Maximum Maximum rr-value:-value: None
The graph???
One Last DefinitionOne Last DefinitionThe graphs of
and
where n is an integer greater than 1, are rose curvesrose curves
cos nθr a
sin nθr a
If n is odd there are n petals;if n is even there are 2n petals
Analyze the graph:
The graph??? How many petals???The graph??? How many petals???
Domain:Domain: , Range:Range: 3,3Symmetry:Symmetry: About the x-axis, y-axis, and origin
Continuity:Continuity: Continuous
Boundedness:Boundedness: Bounded
Asymptotes:Asymptotes: None
Maximum Maximum rr-value:-value: 3
3sin 4r