Chapter 10: Problem 33
\(29-48\) Sketch the curve with the given polar equation. $$r=2(1-\sin \theta), \theta \geqslant 0$$
Short Answer
Expert verified
The curve is a cardioid with a cusp at the origin and opens downward.
Step by step solution
01
Understanding the Polar Equation
We start with the given polar equation \( r = 2(1 - \sin \theta) \). This type of equation is in the form of a ³¢¾±³¾²¹Ã§´Ç²Ô, which typically takes the form \( r = a + b \cdot \sin \theta \) or \( r = a + b \cdot \cos \theta \). Here, \( a = 2 \) and \( b = -2 \).
02
Identifying Key Features
For \( r = a + b \cdot \sin \theta \), the ³¢¾±³¾²¹Ã§´Ç²Ô can take different shapes depending on the relationship between \( a \) and \( b \). Since \( a = b \), this particular equation represents a cardioid without an inner loop. For \( r = 2(1 - \sin \theta) \), we expect a heart-shaped curve.
03
Creating a Table of Values
To sketch the cardioid, calculate \( r \) values for assorted \( \theta \). Starting with \( \theta = 0 \), \( r = 2(1-\sin 0) = 2 \). Continuing, calculate for \( \theta = \frac{\pi}{2} \) where \( \sin \frac{\pi}{2} = 1\), thus \( r = 2(1-1) = 0 \). Similarly, compute values for \( \theta = \pi, \frac{3\pi}{2}, 2\pi \).
04
Plotting the Points
Using the table of values, plot the points calculated in polar coordinates. For instance, when \( \theta = 0 \), plot the point at \( (2, 0) \). At \( \theta = \frac{\pi}{2} \), plot the point at the origin \( (0, \frac{\pi}{2}) \). Repeat for other values: \( (2, \pi), (4, 3\pi/2), (2, 2\pi) \).
05
Drawing the Curve
Connect the plotted points, ensuring the curve passes smoothly through each, mimicking the cardioid shape. The graph will have a cusp at the origin when \( \theta = \frac{\pi}{2} \), looping outwards and forming the heart shape typical of a cardioid, opening towards the negative y-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
³¢¾±³¾²¹Ã§´Ç²Ô
In polar coordinates, a ³¢¾±³¾²¹Ã§´Ç²Ô is a fascinating type of curve that arises from specific polar equations. It appears in the form of either \( r = a + b \cdot \sin \theta \) or \( r = a + b \cdot \cos \theta \), where \( a \) and \( b \) are constants. The shape of a ³¢¾±³¾²¹Ã§´Ç²Ô can vary greatly:
- If \( |a| > |b| \), the ³¢¾±³¾²¹Ã§´Ç²Ô has a dimple.
- If \( |a| = |b| \), it forms a cardioid, which is a special ³¢¾±³¾²¹Ã§´Ç²Ô.
- If \( |a| < |b| \), the ³¢¾±³¾²¹Ã§´Ç²Ô has an inner loop.
Cardioid
A cardioid is a special type of ³¢¾±³¾²¹Ã§´Ç²Ô with a distinct heart-like shape. This curve emerges when \( a = b \) in the ³¢¾±³¾²¹Ã§´Ç²Ô's equation, specifically in forms like \( r = a + a \cdot \sin \theta \) or \( r = a + a \cdot \cos \theta \):
- The point of the heart, known as the cusp, often lies at the origin when expressed as \( r = a(1 - \sin \theta) \) or elsewhere depending on trigonometric function used.
- The cardioid curves smoothly around, indicative of a smooth, continuous loop, unlike other ³¢¾±³¾²¹Ã§´Ç²Ô forms with loops or dimples.
Graphing Polar Curves
Polar coordinates provide a unique method of graphing that focuses on angles and radii rather than traditional x and y axes. When graphing polar curves, follow a step-by-step approach:
- Start by understanding the polar equation and identifying its type, such as a ³¢¾±³¾²¹Ã§´Ç²Ô or cardioid.
- Calculate the radius \( r \) for various angles \( \theta \), creating a table of values.
- Plot these points on polar graph paper, respecting the angle and distance from the pole (origin) as defined by \( r \).
- Connect these plotted points smoothly to reveal the curve's shape.