Chapter 8: Problem 47
Give a complete graph of each polar equation. Also identify the type of polar graph. $$r=3+\cos \theta$$
Short Answer
Expert verified
The graph is a ³¢¾±³¾²¹Ã§´Ç²Ô with an inner loop.
Step by step solution
01
- Identify the General Form
The given polar equation is written as: \[ r = 3 + \cos \theta \]Recognize that it is in the form of: \[ r = a + b \cos \theta \]where \(a = 3\) and \(b = 1\)
02
- Determine the Type of Polar Graph
The polar equation \(r = a + b \cos \theta\) describes a ³¢¾±³¾²¹Ã§´Ç²Ô. Based on the relationship between \(a\) and \(b\), identify the type of ³¢¾±³¾²¹Ã§´Ç²Ô: Since \(|b| < |a|\) (\(1 < 3\)), the ³¢¾±³¾²¹Ã§´Ç²Ô does not have an inner loop. This specific graph is called a ³¢¾±³¾²¹Ã§´Ç²Ô with an inner loop.
03
- Calculate Critical Points
Find the maximum and minimum values of \(r\) by plugging in values of \(\theta\): When \( \theta = 0\): \[ r = 3 + \cos 0 = 3 + 1 = 4 \]When \( \theta = \pi\): \[ r = 3 + \cos \pi = 3 - 1 = 2 \]
04
- Plot the Polar Points
Plot the points for several values of \(\theta\) (such as 0, \(\pi/2\), \(\pi\), and \(3\pi/2\)) to understand the overall shape. For example, for \(\theta = \pi/2\) and \(\theta = 3\pi/2\), \[ r = 3 + \cos (\pi/2) = 3 + 0 = 3 \]
05
- Sketch the Graph
With the calculated points, sketch the complete graph of the polar equation \(r = 3 + \cos \theta\). The resulting graph should resemble a ³¢¾±³¾²¹Ã§´Ç²Ô with an inner loop, extending farther on the right and creating a dimple on the left relative to 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' comes from the French word for snail. ³¢¾±³¾²¹Ã§´Ç²Ôs are a special type of polar graph characterized by their distinctive shape. The general form of the equation for a ³¢¾±³¾²¹Ã§´Ç²Ô is . Here, 'a' and 'b' are constants that determine the shape of the ³¢¾±³¾²¹Ã§´Ç²Ô. Depending on the values of 'a' and 'b', it can have different appearances:
For the given equation , since and , the resulting graph is a ³¢¾±³¾²¹Ã§´Ç²Ô without an inner loop. However, it will show a 'dimpling' effect where the curve indents but does not loop.
- If , the ³¢¾±³¾²¹Ã§´Ç²Ô has an inner loop.
- If , the ³¢¾±³¾²¹Ã§´Ç²Ô will touch the pole but not loop through it.
- If , the ³¢¾±³¾²¹Ã§´Ç²Ô will be a significantly distorted shape without any loops.
For the given equation , since and , the resulting graph is a ³¢¾±³¾²¹Ã§´Ç²Ô without an inner loop. However, it will show a 'dimpling' effect where the curve indents but does not loop.
Polar Coordinates
To fully understand ³¢¾±³¾²¹Ã§´Ç²Ô graphs, it's important to understand polar coordinates. Unlike regular Cartesian coordinates which use to plot points, polar coordinates use . Here ‘r’ represents the distance from the pole (origin) and is the angle measured counter-clockwise from the positive x-axis. This way of plotting is especially helpful for capturing circular and spiral patterns. ³¢¾±³¾²¹Ã§´Ç²Ôs, being one such pattern, rely on this system to showcase their unique shapes.
Plotting Polar Equations
Plotting polar equations like involves several crucial steps:1. **Identify the form**: Notice the form of the equation. Here, it's a standard form of a ³¢¾±³¾²¹Ã§´Ç²Ô where and .
2. **Determine type**: Based on the and values, classify the type of ³¢¾±³¾²¹Ã§´Ç²Ô. The given equation results in a ³¢¾±³¾²¹Ã§´Ç²Ô without an inner loop.
3. **Calculate key points**: Find the maximum and minimum by substituting key values. For instance, at and at . This tells us the farthest and closest points from the pole.
4. **Plot points**: Choose various values like , , and to find corresponding values. This gives a general shape. For example, at and at .
5. **Draw graph**: Connect plotted points smoothly to sketch the ³¢¾±³¾²¹Ã§´Ç²Ô. The graph will reflect its distinctive shape, showing how it extends and dimples based on the calculations.
2. **Determine type**: Based on the and values, classify the type of ³¢¾±³¾²¹Ã§´Ç²Ô. The given equation results in a ³¢¾±³¾²¹Ã§´Ç²Ô without an inner loop.
3. **Calculate key points**: Find the maximum and minimum by substituting key values. For instance, at and at . This tells us the farthest and closest points from the pole.
4. **Plot points**: Choose various values like , , and to find corresponding values. This gives a general shape. For example, at and at .
5. **Draw graph**: Connect plotted points smoothly to sketch the ³¢¾±³¾²¹Ã§´Ç²Ô. The graph will reflect its distinctive shape, showing how it extends and dimples based on the calculations.