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Express the column matrix b as a linear combination of the columns of \(A\) $$A=\left[\begin{array}{rrr} 1 & 1 & -5 \\ 1 & 0 & -1 \\ 2 & -1 & -1 \end{array}\right], \quad \mathbf{b}=\left[\begin{array}{l} 3 \\ 1 \\ 0 \end{array}\right]$$

Short Answer

Expert verified
The column matrix \(b\) can be expressed as a linear combination of the columns of \(A\) in which coefficients are elements of vector \(x = \begin{bmatrix}1\2\0\end{bmatrix}\)

Step by step solution

01

Identify the given matrices

We have the matrix \(A =\begin{bmatrix} 1 & 1 & -5 \1 & 0 & -1 \2 & -1 & -1 \end{bmatrix}\) and column matrix \(b =\begin{bmatrix}3 \1 \0 \end{bmatrix}\)
02

Formulate the system of equations

Express \(b\) as a linear combination of the matrix \(A\)'s columns. This can be expressed by the equation: \(Ax = b\) where \(A\) is the given matrix, \(x\) is the vector we are looking for and \(b\) is the given vector. We can write three equations corresponding to the rows of the equation \(Ax = b\): \(x_1 + x_2 - 5x_3 = 3,\) \(x_1 - x_3 = 1,\) \(2x_1 - x_2 - x_3 = 0.\)
03

Solve the system of equations

Solving the system of equations yields: \(x_1 = 1,\) \(x_2 = 2,\) and \(x_3 = 0.\)
04

Form the vector \(x\)

After we find the values of \(x_1, x_2,\) and \(x_3\), the vector \(x\) can be written as \(x =\begin{bmatrix}1\2\0\end{bmatrix}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

System of Equations
A system of equations is a collection of two or more equations with a common set of variables. These equations require a solution that satisfies every equation in the system. In the context of the exercise, the system of equations is derived from the expression \(Ax = b\). Here, each row of matrix \(A\) forms an equation, contributing to a complete system of equations. The main task is to find values for the vector \(x\) that satisfies all these equations simultaneously.

When expressing the column matrix \(b\) as a linear combination of the columns of \(A\), a system of equations is essentially established. Each component of \(b\) corresponds to a combination derived from the values in matrix \(A\), multiplied by components of \(x\). Solving this system involves:
  • Identifying each equation formed from the rows.
  • Solving the equations to find the values of \(x_1, x_2,\) and \(x_3\).
These solutions are crucial in understanding how linear combinations work in the context of matrices.
Column Matrix
A column matrix is simply a matrix consisting of a single column of numbers. It represents a vector in matrix terminology and can be an integral part of linear algebra calculations.

In the exercise, the column matrix \(b\) is represented as \(\begin{bmatrix}3\1\0\end{bmatrix}\). This means it has entries, or elements, arranged vertically with three rows. Each row corresponds to a separate equation when breaking down the system of equations from the previous step.

Column matrices are essential in matrices operations involving systems of linear equations and in linear combinations, as each column matrix can represent a singular variable or outcome in the context of vector spaces.
Matrix Multiplication
Matrix multiplication is a fundamental operation in linear algebra where two matrices are multiplied to produce another matrix. This involves the dot product of rows of the first matrix and columns of the second matrix.

In the context of the problem, calculating \(Ax\) involves multiplying matrix \(A\) with vector \(x\). This multiplication results in a new column matrix that we set equal to \(b\). The components of the resulting matrix are made by:
  • Multiplying corresponding entries across rows of \(A\) and columns of \(x\).
  • Summing those products to form each element of the column matrix.

Matrix multiplication is crucial because it allows for the formulation and solving of systems of equations, turning a seemingly complex problem into a set of simpler calculations. This method is widely used to solve linear algebra problems and model real-world systems in engineering, physics, computer science, and economics.

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Most popular questions from this chapter

Prove that \(A\) is idempotent if and only if \(A^{T}\) is idempotent. Getting Started: The phrase "if and only if" means that you have to prove two statements: 1\. If \(A\) is idempotent, then \(A^{T}\) is idempotent. 2\. If \(A^{T}\) is idempotent, then \(A\) is idempotent. (i) Begin your proof of the first statement by assuming that \(A\) is idempotent. (ii) This means that \(A^{2}=A\) (iii) Use the properties of the transpose to show that \(A^{T}\) is idempotent. (iv) Begin your proof of the second statement by assuming that \(A^{T}\) is idempotent.

The columns of matrix \(T\) show the coordinates of the vertices of a triangle. Matrix \(A\) is a transformation matrix. $$A=\left[\begin{array}{rr} 0 & -1 \\ 1 & 0 \end{array}\right], \quad T=\left[\begin{array}{lll} 1 & 2 & 3 \\ 1 & 4 & 2 \end{array}\right]$$ (a) Find \(A T\) and \(A A T .\) Then sketch the original triangle and the two transformed triangles. What transformation does \(A\) represent? (b) A triangle is determined by \(A A T .\) Describe the transformation process that produces the triangle determined by \(A T\) and then the triangle determined by \(T\)

Determine whether each statement is true or false. If a statement is true, give a reason or cite an appropriate statement from the text. If a statement is false, provide an example that shows the statement is not true in all cases or cite an appropriate statement from the text. (a) The zero matrix is an elementary matrix. (b) A square matrix is nonsingular if it can be written as the product of elementary matrices. (c) \(A \mathbf{x}=O\) has only the trivial solution if and only if \(A \mathbf{x}=\mathbf{b}\) has a unique solution for every \(n \times 1\) column matrix b.

The market research department at a manufacturing plant determines that \(20 \%\) of the people who purchase the plant's product during any month will not purchase it the next month. On the other hand, \(30 \%\) of the people who do not purchase the product during any month will purchase it the next month. In a population of 1000 people, 100 people purchased the product this month. How many will purchase the product next month? In 2 months?

Prove the associative property of scalar multiplication: \((c d) A=c(d A)\)

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