Chapter 11: Problem 23
Find an equation in rectangular coordinates for the equation given in cylindrical coordinates, and sketch its graph. \(\theta=\pi / 6\)
Short Answer
Expert verified
In rectangular coordinates, the equation \(\theta=\pi/6\) becomes \(y=\sqrt{3}x\). This is a line rising from the origin with a slope of \(\sqrt{3}\), extending indefinitely in the z-direction.
Step by step solution
01
Convert Cylindrical to Rectangular Coordinates
Starting from the conversion formula for x and y in terms of r and theta, we know that \(x= r\cos(\theta)\) and \(y = r\sin(\theta)\). In our case, \(\theta\) is fixed at the value \(\pi / 6\). Plugging this into our formulae for x and y, we get \(x= r\cos(\pi / 6)\) and \(y = r\sin(\pi / 6)\). For any arbitrary r, these equations will provide x and y values that satisfy \(\theta = \pi / 6\).
02
Express equation in terms of x and y
Now that we have the x and y values in terms of r, the equation \(\theta=\pi / 6\) can be expressed in terms of x and y. Firstly, we know that \(\tan(\theta) = \frac{y}{x}\), thus our equation becomes \(\tan(\pi / 6) = \frac{y}{x}\). This simplifies to \(\sqrt{3}/3 = \frac{y}{x}\), which rearranged gives \(y=\sqrt{3}x\).
03
Graphing the Equation
This equation in rectangular coordinates represents a straight line passing through the origin with a slope of \(\sqrt{3}\). The line can be sketched on the xy plane starting from the origin and rising at a slope of \(\sqrt{3}\). Be sure to note that this is a 3D line, as there was no z-coordinate restriction, meaning the line extends infinitely in the positive and negative z-directions.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Rectangular Coordinates
In the world of geometry, rectangular coordinates are incredibly useful. They define a point in a plane using two numbers — typically referred to as (x, y).
The x-coordinate measures how far along the horizontal axis a point is, while the y-coordinate measures how far along the vertical axis a point is.
This is often our go-to method for pinpointing precise locations on the Cartesian plane. One big advantage of using rectangular coordinates is their simplicity when dealing with linear equations or functions in two-dimensional plots.
The x-coordinate measures how far along the horizontal axis a point is, while the y-coordinate measures how far along the vertical axis a point is.
This is often our go-to method for pinpointing precise locations on the Cartesian plane. One big advantage of using rectangular coordinates is their simplicity when dealing with linear equations or functions in two-dimensional plots.
- They make it easy to visualize solutions and relationships between variables.
- Using x and y, we can directly graph equations on a straightforward grid.
Cylindrical Coordinates
Cylindrical coordinates blend aspects of both polar and rectangular coordinates. They're mainly used in three-dimensional space.
Unlike the two-coordinate system in a plane, cylindrical coordinates require three parameters:
Unlike the two-coordinate system in a plane, cylindrical coordinates require three parameters:
- : The radial distance from the origin, similar to the polar radius.
- \(\theta\): The angular coordinate, showing how far the line angle is swept from the positive x-axis.
- \: The same z from rectangular coordinates, providing height.
Equation Conversion
Converting between coordinate systems is a vital skill, especially between cylindrical and rectangular coordinates.
This usually involves using specific formulas like those for converting polar to Cartesian coordinates. For example:
By expressing \(\tan(\theta) = \frac{y}{x}\), it transitioned seamlessly into a line in the rectangular plane.
This usually involves using specific formulas like those for converting polar to Cartesian coordinates. For example:
- \(x = r\cos(\theta)\) and \(y = r\sin(\theta)\)
By expressing \(\tan(\theta) = \frac{y}{x}\), it transitioned seamlessly into a line in the rectangular plane.
Graphing Equations
The magic of graphing equations is that it transforms abstract numbers and symbols into something visual.
In rectangular coordinates, every point corresponds to a unique pair of x and y values. When we have a line equation like \(y = \sqrt{3}x\), it tells us exactly how the x and y coordinates relate:
In rectangular coordinates, every point corresponds to a unique pair of x and y values. When we have a line equation like \(y = \sqrt{3}x\), it tells us exactly how the x and y coordinates relate:
- The slope, \(\sqrt{3}\), shows the steepness of the line.
- The line crosses the origin (0,0), indicating it passes through this central point.