Chapter 10: Problem 17
Sketch the polar curve and find polar equations of the tangent lines to the curve at the pole. $$ r=1-2 \cos \theta $$
Short Answer
Expert verified
The tangent lines at the pole occur at \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \).
Step by step solution
01
Understand the Polar Curve
The polar equation given is \( r = 1 - 2\cos\theta \). This equation represents a ³¢¾±³¾²¹Ã§´Ç²Ô. To determine the shape, observe the coefficient of \( \cos \theta \): it is larger than 1, suggesting that the ³¢¾±³¾²¹Ã§´Ç²Ô has an inner loop.
02
Determine When the Curve Passes Through the Pole
The curve passes through the pole when \( r = 0 \). Setting \( 1 - 2\cos\theta = 0 \), we solve \( 2\cos\theta = 1 \), giving \( \cos\theta = \frac{1}{2} \). Hence, \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \).
03
Find the Slope of the Tangent at the Pole
The polar tangents at the pole correspond to where \( r = 0 \). Here, check derivatives: \( dr = (2\sin\theta)d\theta \). Substitute \( \theta = \frac{\pi}{3} \) and \( \frac{5\pi}{3} \) to find slopes. At these angles, differentiate to confirm tangency direction is along \( \theta \).
04
Write the Tangent Line Equations in Polar Coordinates
At the pole points \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \), the tangents are lines through the pole at these angles. The equations are simply \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \).
05
Visualize and Sketch the Curve with Tangents
Sketch the ³¢¾±³¾²¹Ã§´Ç²Ô curve noting it intersects the pole at \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \). Draw straight lines through the origin corresponding to these angles showing tangents at the pole.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
³¢¾±³¾²¹Ã§´Ç²Ô
The term "³¢¾±³¾²¹Ã§´Ç²Ô" might sound fancy, but it's actually just a type of polar curve that looks similar to a distorted circle. These curves are defined by equations of the form \( r = a + b\cos\theta \) or \( r = a + b\sin\theta \). Depending on the relationship between \( a \) and \( b \), the ³¢¾±³¾²¹Ã§´Ç²Ô can have different forms:
- When \( b > a \), it features an inner loop.
- If \( b = a \), it appears heart-shaped, also known as a cardioid.
- When \( a > b \), it bulges outward without any loops.
Tangent Line Equations
Tangent line equations in polar coordinates differ a bit from their Cartesian counterparts. They are used to find lines that just touch a curve at a point without crossing it. In our task, we are specifically interested in finding tangent lines at the pole, which is the origin in polar coordinates.For the polar curve \( r = 1 - 2\cos\theta \), the tangents at the pole are found by considering where \( r = 0 \). Setting \( 1 - 2\cos\theta = 0 \), implies that \( \cos\theta = \frac{1}{2} \). This gives us the angles \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \).At these angles, the equations for the tangents are simply the straight lines given by these angles radiating from the origin. Thus, the tangent line equations are \( \theta = \frac{\pi}{3} \) and \( \theta = \frac{5\pi}{3} \). These represent the direction of the tangent at the pole without specifying a distance or path, which is characteristic in polar coordinates.
Polar Coordinates
Polar coordinates are a way of representing points in a plane through distance and angle, rather than the traditional x and y coordinates. Each point is defined by \( (r, \theta) \) where:
- \( r \) is the radial distance from the origin (also called the pole),
- \( \theta \) is the angle measured from the positive x-axis (known as the polar axis).