Table of contents
- 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 21
Textbook Question
In Exercises 13–34, test for symmetry and then graph each polar equation. r = 1 + 2 cos θ
Verified step by step guidance1
Recall the three common tests for symmetry in polar coordinates: symmetry about the polar axis (x-axis), symmetry about the line \( \theta = \frac{\pi}{2} \) (y-axis), and symmetry about the pole (origin).
To test symmetry about the polar axis, replace \( \theta \) with \( -\theta \) in the equation \( r = 1 + 2 \cos \theta \) and check if the equation remains unchanged.
To test symmetry about the line \( \theta = \frac{\pi}{2} \), replace \( \theta \) with \( \pi - \theta \) and check if the equation remains unchanged.
To test symmetry about the pole, replace \( r \) with \( -r \) and \( \theta \) with \( \theta + \pi \) and check if the equation remains unchanged.
After determining the symmetries, plot points for various values of \( \theta \) (for example, \( 0, \frac{\pi}{6}, \frac{\pi}{4}, \frac{\pi}{2}, \pi \), etc.) by calculating \( r \) and then sketch the graph accordingly.
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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 and an angle (r, θ) instead of Cartesian (x, y). Understanding how to interpret and plot polar equations like r = 1 + 2 cos θ is essential for graphing curves in the polar plane.
Recommended video:
Intro to Polar Coordinates
Symmetry Tests in Polar Graphs
Testing symmetry in polar graphs involves checking if the equation remains unchanged under transformations: θ → -θ (symmetry about the polar axis), θ → π - θ (symmetry about the line θ = π/2), and r → -r with θ → θ + π (symmetry about the pole). This helps simplify graphing by identifying mirrored parts.
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Cardioids
Graphing Polar Equations Involving Cosine
Polar equations with cosine terms, such as r = 1 + 2 cos θ, often produce limaçon shapes. Recognizing how the cosine function affects the radius for different angles allows for accurate plotting and understanding of the curve's features like loops or dimpled shapes.
Recommended video:
Introduction to Common Polar Equations
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Related Practice
Textbook Question
In Exercises 13–34, test for symmetry and then graph each polar equation.r = 2 + 2 cos θ
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