Chapter 7: Problem 51
Find the volume of the parallelepiped for which the given vectors are three edges. $$ \mathbf{a}=\mathbf{i}+\mathbf{j}, \mathbf{b}=-\mathbf{i}+4 \mathbf{j}, \mathbf{c}=2 \mathbf{i}+2 \mathbf{j}+2 \mathbf{k} $$
Short Answer
Expert verified
The volume of the parallelepiped is 10.
Step by step solution
01
Represent Vectors as Columns
Represent vectors \( \mathbf{a} \), \( \mathbf{b} \), and \( \mathbf{c} \) as columns in a 3x3 matrix. This is the initial setup: \[\mathbf{a} = \begin{pmatrix} 1 \ 1 \ 0 \end{pmatrix},\mathbf{b} = \begin{pmatrix} -1 \ 4 \ 0 \end{pmatrix},\mathbf{c} = \begin{pmatrix} 2 \ 2 \ 2 \end{pmatrix}\]
02
Construct the Matrix
The matrix formed by the vectors \( \mathbf{a} \), \( \mathbf{b} \), and \( \mathbf{c} \) is as follows: \[\begin{bmatrix} 1 & -1 & 2 \ 1 & 4 & 2 \ 0 & 0 & 2 \end{bmatrix}\]
03
Calculate the Determinant
Calculate the determinant of the matrix to find the volume. The determinant is calculated as follows: \[|\begin{vmatrix} 1 & -1 & 2 \ 1 & 4 & 2 \ 0 & 0 & 2 \end{vmatrix}| \]Using cofactor expansion along the third column: \[= 2 \left( \begin{vmatrix} 1 & -1 \ 1 & 4 \end{vmatrix} \right) = 2(4 + 1) = 2 \times 5 = 10\]
04
Interpret the Result
The determinant calculated is 10, which represents the volume of the parallelepiped formed by vectors \( \mathbf{a} \), \( \mathbf{b} \), and \( \mathbf{c} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Calculus
Vector Calculus is a branch of mathematics that deals with vectors and operations on vector spaces. It helps us understand physical quantities like force and velocity, which have both magnitude and direction.
- Vectors: Basic building blocks in vector calculus. They are entities with both direction and magnitude represented in Euclidean space.
- Applications: Useful in physics and engineering, such as calculating trajectories, fluid dynamics, and electromagnetism.
Determinants
Determinants play a pivotal role in various mathematical computations. They are crucial in linear algebra for solving systems of linear equations and analyzing matrix properties.
- Matrix Requirement: Determinants are computed for square matrices (matrices with the same number of rows and columns).
- Properties of Determinants: They can provide information on the volume scaling factor of linear transformations.
- Significance: A zero determinant indicates a matrix that doesn't have an inverse, representing parallel or dependent vectors in space.
Matrix Representation
Matrices are a fundamental part of mathematics and are used for numerous calculations in vector calculus. They compactly organize data, making it easier to perform complex operations.
- Column Vectors: Each vector in a 3-dimensional space can be represented as a column in a matrix, preserving its structure.
- Matrix Formation: By arranging vectors as columns, we can visualize geometric transformations and solve for volumes through determinant calculations.
Cofactor Expansion
Cofactor Expansion, also known as Laplace Expansion, is a method used to calculate the determinant of a matrix. It involves breaking down a matrix into smaller parts, making it easier to manage calculations for larger matrices.
- Usefulness: Particularly useful for calculating determinants of 3x3 or larger matrices by expanding along a row or column.
- Steps: Select a row or column, remove it to form a smaller matrix, calculate its determinant, and multiply by the signed cofactor.
- Alternating Signs: Remember that the cofactors alternate signs (+/-) based on their position.