Chapter 9: Problem 50
Convert the polar equation to rectangular coordinates. $$ r=6 \cos \theta $$
Short Answer
Expert verified
The rectangular form is \\(x^2 - 6x + y^2 = 0\\) or \\( (x-3)^2 + y^2 = 9\\).
Step by step solution
01
Understand Polar and Rectangular Coordinates
In polar coordinates, a point is represented by \(r, \theta\), where \(r\) is the distance from the origin and \(\theta\) is the angle from the positive x-axis. To convert to rectangular coordinates \(x, y\), use the conversions \(x = r \cos \theta\) and \(y = r \sin \theta\).
02
Substitute Polar Equation into Rectangular Formula
Our given equation is \(r = 6 \cos \theta\). Multiply both sides by \(r\): \[ r^2 = 6r \cos \theta \]
03
Use Rectangular Conversion Formula
Recall that \(r^2 = x^2 + y^2\) and \(r \cos \theta = x\). Substitute these into the equation: \[ x^2 + y^2 = 6x \]
04
Rearrange to Rectangular Equation Form
Rearrange the equation to place all terms on one side: \[ x^2 - 6x + y^2 = 0 \]
05
Complete the Square (Optional)
If needed, complete the square for the \(x\) terms to further simplify or analyze the equation: Add and subtract \(9\) (which is \(\left( \frac{6}{2} \right)^2\)) to the equation: \[(x-3)^2 + y^2 = 9\]This represents a circle with center (3, 0) and radius 3.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar coordinates offer a unique way of representing points in a plane through a combination of distance and direction. In this system, every point is described by two values: \( r \) and \( \theta \).
- \( r \) represents the distance from the origin (like the radius of a circle).
- \( \theta \) denotes the angle measured from the positive x-axis.
Rectangular Coordinates
Rectangular coordinates are the more traditional way of plotting points on a graph, utilizing horizontal and vertical distances. These are denoted as \((x, y)\).
- \( x \): The horizontal distance from the y-axis (positive towards the right).
- \( y \): The vertical distance from the x-axis (positive upwards).
Coordinate Transformation
Switching between polar and rectangular coordinates is a valuable technique, especially in mathematical fields where different perspectives or angles help clarify relationships.
- To transform from polar to rectangular, use:
- \( x = r \cos \theta \)
- \( y = r \sin \theta \)
- Conversely, for transforming from rectangular to polar, use:
- \( r = \sqrt{x^2 + y^2} \)
- \( \theta = \tan^{-1}(y/x) \)
Equation Conversion
When converting an equation from polar to rectangular coordinates, like the original exercise \( r = 6 \cos \theta \), you substitute polar terms with their rectangular equivalents.
- Inicio: Multiply both sides by \( r \) yielding \( r^2 = 6r \cos \theta \).
- Step: Replace terms using known conversions. For example, use \( r^2 = x^2 + y^2 \) and \( r \cos \theta = x \).
- Resultados: Simplify into a typical rectangular equation, such as \( x^2 + y^2 = 6x \).
- Further: Optional simplification steps, like completing the square, reveal useful information (e.g., circles, ellipses).