Chapter 14: Problem 19
Find the minimum distance from the surface \(x^{2}-y^{2}-z^{2}=1\) to the origin.
Short Answer
Expert verified
The minimum distance is 1.
Step by step solution
01
Understand the Problem
We need to find the minimum distance from the surface \(x^2 - y^2 - z^2 = 1\) to the origin \((0, 0, 0)\). The surface defined is a hyperboloid of one sheet. To solve this, we'll express the distance formula, subject to the condition given by the surface.
02
Express the Distance Formula
The squared distance \(D\) from a point \((x, y, z)\) on the surface to the origin is given by \(D = x^2 + y^2 + z^2\). We aim to minimize this distance.
03
Use the Constraint
The point \((x, y, z)\) also needs to satisfy the surface equation \(x^2 - y^2 - z^2 = 1\). Therefore, our problem is to minimize \(x^2 + y^2 + z^2\) subject to \(x^2 - y^2 - z^2 = 1\).
04
Formulate using Lagrange Multipliers
We use the method of Lagrange multipliers. We set up the Lagrangian as \(L(x, y, z, \lambda) = x^2 + y^2 + z^2 + \lambda (1 - x^2 + y^2 + z^2)\).
05
Derive the Equations
Calculate the partial derivatives and set them to zero:- \(L_x = 2x - 2x\lambda = 0\)- \(L_y = 2y + 2y\lambda = 0\)- \(L_z = 2z + 2z\lambda = 0\)- \(L_\lambda = 1 - x^2 + y^2 + z^2 = 0\).
06
Solve the System of Equations
From the equations, it's clear that:- \(x(1 - \lambda) = 0\)- \(y(1 + \lambda) = 0\)- \(z(1 + \lambda) = 0\)These suggest that for non-zero \(x\), \(\lambda = 1\), and for non-zero \(y\) and \(z\), \(\lambda = -1\). We analyze these conditions under the constraint \(x^2 - y^2 - z^2 = 1\).
07
Investigate Cases
For \(x = 0\), \(y^2 + z^2 = -1\) is not possible as it's negative. Checking \(y = 0, z = 0\) we have, \(x^2 = 1\) leading to \(x = \pm 1\). This gives us two points \( (1, 0, 0) \) and \( (-1, 0, 0) \).
08
Calculate the Minimum Distance
For points \((1, 0, 0)\) and \((-1, 0, 0)\), the distance is \(\sqrt{1^2 + 0^2 + 0^2} = 1\). Hence, the minimum distance from the origin is 1.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hyperboloid of One Sheet
A hyperboloid of one sheet is an intriguing surface in three-dimensional space. It's defined by the equation \(x^2 - y^2 - z^2 = 1\). Visually, this surface looks somewhat like an elongated, double-coned shape that is connected in the middle. This unique structure is symmetric around all three coordinate axes. This symmetry plays a role in mathematical problems involving this surface.Some characteristics of a hyperboloid of one sheet include:
- It extends indefinitely in all three dimensions.
- The cross-sections taken parallel to any foreground plane (like \(xy, yz,\) or \(xz\)) will appear as hyperbolas.
- If you cut it perpendicular to its axis of symmetry, you'll observe circles.
Optimization
Optimization involves finding the best possible solution to a problem, often under given constraints. In this context, we want to minimize a particular function while respecting the constraints imposed by another equation.In our exercise, optimization is achieved through the use of Lagrange multipliers. This method takes a complex problem and transforms it into a system of equations that are easier to manage. By doing so, we keep the constraints intact while exploring potential solutions.Here's a simplified breakdown of the Lagrange multipliers method:
- Identify the function you want to minimize or maximize. In our case, it's the squared distance \(x^2 + y^2 + z^2\).
- Consider the constraint given by another equation, here being the hyperboloid equation \(x^2 - y^2 - z^2 = 1\).
- Create a Lagrangian function, which includes the function to be optimized and integrates the constraint with a multiplier \(\lambda\).
- Find the partial derivatives of this Lagrangian and set them to zero to find critical points.
Distance Minimization
The goal of distance minimization is to find the shortest distance from a point to a surface. For our exercise, the focus was on minimizing the distance from the hyperboloid of one sheet to the origin.We measure the distance between a variable point \((x, y, z)\) on the surface to the origin. This is described by the formula \(\sqrt{x^2 + y^2 + z^2}\). For optimization, this is simplified to considering the squared distance, making the function easier to work with.Here's how distance minimization works in this case:
- Using the surface's equation, apply the method of Lagrange multipliers to ensure any point considered belongs to the surface.
- After solving the equations, determine feasible solutions that satisfy both the constraint and fulfill distance requirements.
- Calculate the distance for each viable solution to identify the minimum.