Chapter 14: Problem 28
Eliminate the parameters to obtain an equation in rectangular coordinates, and describe the surface. $$ \begin{array}{l}{x=u \cos v, y=u^{2}, z=u \sin v \text { for } 0 \leq u \leq 2 \text { and }} \\ {0 \leq v<2 \pi}\end{array} $$
Short Answer
Expert verified
The surface is a paraboloid described by \( x^2 + z^2 = y \).
Step by step solution
01
Identify the Given Parametric Equations
The parametric equations are given as: \( x = u\cos v \), \( y = u^2 \), and \( z = u\sin v \). We seek to eliminate the parameters \( u \) and \( v \) to find a single equation in terms of \( x, y, \) and \( z \).
02
Eliminate Parameter \( v \) Using Trigonometric Identity
To eliminate \( v \), use the identity \( \cos^2 v + \sin^2 v = 1 \). Express \( \cos v \) as \( \cos v = \frac{x}{u} \) and \( \sin v \) as \( \sin v = \frac{z}{u} \). Substitute these into the identity:\[\left(\frac{x}{u}\right)^2 + \left(\frac{z}{u}\right)^2 = 1\]
03
Simplify the Equation
Multiply the entire equation by \( u^2 \):\[x^2 + z^2 = u^2\]This expression suggests a way to relate \( u^2 \) directly to \( y \).
04
Substitute \( u^2 \) with \( y \)
From the equation \( y = u^2 \), substitute \( u^2 \) in the equation we derived:\[ x^2 + z^2 = y \]This is the rectangular equation of the surface.
05
Identify the Surface
The equation \( x^2 + z^2 = y \) can be recognized as a paraboloid that opens along the positive y-axis. This confirms the surface is a paraboloid constrained from \( 0 \leq y \leq 4 \) due to \( 0 \leq u \leq 2 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parametric Equations
Parametric equations are a fascinating way to describe geometric objects, by using parameters, rather than expressing coordinates directly. These equations allow us to define a curve or surface in terms of one or more variables. In the given example, the parametric equations involve variables \( u \) and \( v \) to define a surface in three-dimensional space. Here, each coordinate \((x, y, z)\) is a function of \( u \) and \(v\):
- \( x = u \cos v \)
- \( y = u^2 \)
- \( z = u \sin v \)
Rectangular Coordinates
Rectangular coordinates, also known as Cartesian coordinates, are a familiar way of representing points in a plane or space using a coordinate system. In this system, every point has an \( x \), \( y \), and possibly a \( z \) value in a three-dimensional space.To convert parametric equations to a rectangular form, like the equation \( x^2 + z^2 = y \) achieved in the solution, we eliminate the parameters \( u \) and \( v \). By using identities such as \( \cos^2 v + \sin^2 v = 1 \), we convert the parametric form into something more universally understandable, using plain \( x \), \( y \), and \( z \) coordinates.This form allows us to easily identify and describe surfaces or curves with which we're working. When used correctly, rectangular coordinates offer a straightforward way of visualizing and analyzing shapes, making them a vital tool in calculus and other fields.
Paraboloid
One intriguing surface described by the rectangular equation \( x^2 + z^2 = y \) is a paraboloid. A paraboloid is a 3D shape that looks like an umbrella however it can be more rounded at the base or thin and sharp.This specific equation represents a paraboloid that opens upward along the y-axis. More precisely, points on this surface satisfy the condition: as \( x \) and \( z \) move away from the origin, \( y \) increases proportionally, giving the surface its parabolic shape.Key characteristics of this paraboloid include:
- Symmetry around the y-axis, meaning if you rotate it by any angle around this axis, the shape remains unchanged.
- The opening along the y-axis, which defines how the paraboloid extends as you move further from its base.
- Constrained by \( 0 \leq y \leq 4 \) due to \( 0 \leq u \leq 2 \).