In Exercises 27–32, select the representations that do not change the location of the given point. (4, 120°) (−4, 300°)
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- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
9. Polar Equations
Polar Coordinate System
Problem 31
Textbook Question
In Exercises 13–34, test for symmetry and then graph each polar equation. r = 1 − 3 sin θ
Verified step by step guidance1
Recall that to test for symmetry in polar equations, we check three types: symmetry about the polar axis (x-axis), symmetry about the line \( \theta = \frac{\pi}{2} \) (y-axis), and symmetry about the pole (origin).
For symmetry about the polar axis, replace \( \theta \) with \( -\theta \) in the equation and see if the equation remains unchanged. That is, check if \( r = 1 - 3 \sin(-\theta) \) simplifies to the original equation.
For symmetry about the line \( \theta = \frac{\pi}{2} \), replace \( \theta \) with \( \pi - \theta \) and check if the equation remains unchanged. So, check if \( r = 1 - 3 \sin(\pi - \theta) \) simplifies to the original equation.
For symmetry about the pole, replace \( r \) with \( -r \) and \( \theta \) with \( \theta + \pi \), then check if the equation remains unchanged. That is, check if \( -r = 1 - 3 \sin(\theta + \pi) \) can be rearranged to the original form.
After determining the symmetries, sketch the graph by plotting points for various values of \( \theta \) between 0 and \( 2\pi \), using the equation \( r = 1 - 3 \sin \theta \), and then reflect the graph according to the symmetries found.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Polar Coordinates and Equations
Polar coordinates represent points using a radius r and an angle θ from the positive x-axis. Polar equations express r as a function of θ, describing curves in the plane. Understanding how to interpret and plot these equations is essential for graphing polar curves.
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Intro to Polar Coordinates
Symmetry Tests in Polar Graphs
Symmetry in polar graphs can be tested about the polar axis, the line θ = π/2, and the pole (origin). These tests involve substituting θ with -θ, π - θ, or replacing r with -r to check if the equation remains unchanged, helping to identify symmetrical properties of the curve.
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Cardioids
Graphing Polar Equations Involving Sine
Polar equations with sine functions, like r = 1 - 3 sin θ, often produce limaçon or cardioid shapes. Recognizing the effect of the sine term on the radius as θ varies aids in sketching the curve accurately, including identifying loops, petals, or inner loops.
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