Chapter 11: Problem 80
Convert the equation from polar coordinates into rectangular coordinates. $$ \theta=\frac{2 \pi}{3} $$
Short Answer
Expert verified
The polar equation \( \theta = \frac{2\pi}{3} \) converts to the rectangular line equation \( x = -\sqrt{3}y \).
Step by step solution
01
Understand Polar Coordinates
In polar coordinates, a point is represented by \[ (r, \theta) \] where \( r \) is the distance from the origin and \( \theta \) is the angle. The task is to convert the given polar equation into rectangular coordinates (\( x, y \)). We have \( \theta = \frac{2\pi}{3} \) without a specific \( r \) value, which means we have an angle direction but no specific radius.
02
Use Relationship Between Polar and Rectangular Coordinates
The relationships between polar and rectangular coordinates are given by:\[ x = r \cos(\theta) \]\[ y = r \sin(\theta) \]where \( x \) and \( y \) are the rectangular coordinates. Since no \( r \) is specified, focus on expressing \( \cos(\theta) \) and \( \sin(\theta) \) to find the line corresponding to \( \theta = \frac{2\pi}{3} \).
03
Calculate Trigonometric Values
First, find \( \cos(\theta) \) and \( \sin(\theta) \) for \( \theta = \frac{2\pi}{3} \). These are fundamental trigonometric positions:\[ \cos\left(\frac{2\pi}{3}\right) = -\frac{1}{2} \]\[ \sin\left(\frac{2\pi}{3}\right) = \frac{\sqrt{3}}{2} \]
04
Rewrite Equation in Rectangular Form
From the known relationships:- \( x = r \cos(\theta) \) becomes \( -x/2 \) when in terms of the given angle.- \( y = r \sin(\theta) \) becomes \( y\sqrt{3}/2 \).Since there’s no given \( r \), these variables relate as \[ y\sqrt{3} = -x \]This can be simplified as\[ \sqrt{3}y = -x \] or \[ x = -\sqrt{3}y \]representing the line through the origin with slope \(-\frac{1}{\sqrt{3}}\).
05
Conclusion: Rectangular Equation
The equation \( \theta = \frac{2\pi}{3} \) in polar coordinates is a line with direction angle only (angle without specific radius). It converts to the rectangular form: \[ x = -\sqrt{3}y \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar coordinates are a way to locate a point in the plane using a distance and an angle. Instead of the familiar
For example, when dealing with circular motion or spiral shapes.
In the exercise at hand, we have a given angle, \(\theta = \frac{2\pi}{3}\), but no specific radius.This implies we are focusing purely on the direction — representing a line rather than a specific point.
- Cartesian system with axes and coordinates
- polar coordinates are given as a pair
- \((r, \theta)\) where:
- \(r\) represents the radial distance from a fixed point called the origin.
- \(\theta\) denotes the angle from a fixed direction, usually measured in radians from the positive x-axis.
For example, when dealing with circular motion or spiral shapes.
In the exercise at hand, we have a given angle, \(\theta = \frac{2\pi}{3}\), but no specific radius.This implies we are focusing purely on the direction — representing a line rather than a specific point.
Rectangular Coordinates
Rectangular coordinates, also known as Cartesian coordinates, are defined by a pair
They allow you to easily calculate distances and angles using algebra and geometry.
The exercise aims to transition from a polar representation where an angle is given, to this format. By doing so, we pinpoint how a direction defined in polar terms transforms into a line equation in rectangular terms.
- \((x, y)\) that describe a point's exact position on a plane using horizontal and vertical axes:
- \(x\) is the horizontal distance from the origin.
- \(y\) is the vertical distance.
They allow you to easily calculate distances and angles using algebra and geometry.
The exercise aims to transition from a polar representation where an angle is given, to this format. By doing so, we pinpoint how a direction defined in polar terms transforms into a line equation in rectangular terms.
Trigonometric Functions
Trigonometric functions are key to translating between polar and rectangular coordinates.
They relate the angles in polar coordinates to the respective x and y positions in rectangular coordinates.
Calculating these gives:
They relate the angles in polar coordinates to the respective x and y positions in rectangular coordinates.
- \(\cos(\theta)\) helps determine the horizontal projection, and \(\sin(\theta)\) the vertical.
Calculating these gives:
- \(\cos\left(\frac{2\pi}{3}\right) = -\frac{1}{2}\), indicating an acute negative horizontal component.
- \(\sin\left(\frac{2\pi}{3}\right) = \frac{\sqrt{3}}{2}\), indicating a positive vertical component.
Coordinate Transformation
Coordinate transformation involves changing the description of a location from one coordinate system to another.
For problems like this exercise, it specifically addresses converting a point or line from polar to rectangular notation.
These relations transform into equations that describe the tilt of the line defined by the angle \(\theta = \frac{2\pi}{3}\).
This slide in representation gives equation \(x = -\sqrt{3}y\), a mathematical shift that helps visualize the directional nature of the original polar statement.
For problems like this exercise, it specifically addresses converting a point or line from polar to rectangular notation.
- The process utilizes relationships:
- \(x = r \cos(\theta)\)
- \(y = r \sin(\theta)\)
These relations transform into equations that describe the tilt of the line defined by the angle \(\theta = \frac{2\pi}{3}\).
This slide in representation gives equation \(x = -\sqrt{3}y\), a mathematical shift that helps visualize the directional nature of the original polar statement.