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Ch. 6 - Matrices and Determinants
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 19

For Exercises 11–22, use Cramer's Rule to solve each system. {3x−4y=42x+2y=12\(\begin{cases}\) 3x - 4y = 4 \\ 2x + 2y = 12 \(\end{cases}\)

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Write the system of equations in standard form: \(\begin{cases} 3x - 4y = 4 \\ 2x + 2y = 12 \end{cases}\)
Identify the coefficients for the variables and constants: \(A = \begin{bmatrix} 3 & -4 \\ 2 & 2 \end{bmatrix}\), \(\mathbf{x} = \begin{bmatrix} x \\ y \end{bmatrix}\), \(\mathbf{b} = \begin{bmatrix} 4 \\ 12 \end{bmatrix}\)
Calculate the determinant of matrix \(A\), denoted as \(D\): \(D = \det(A) = (3)(2) - (-4)(2)\)
Form matrices \(A_x\) and \(A_y\) by replacing the respective columns of \(A\) with the constants vector \(\mathbf{b}\): \(A_x = \begin{bmatrix} 4 & -4 \\ 12 & 2 \end{bmatrix}\), \(A_y = \begin{bmatrix} 3 & 4 \\ 2 & 12 \end{bmatrix}\)
Calculate the determinants \(D_x = \det(A_x)\) and \(D_y = \det(A_y)\), then use Cramer's Rule to find the solutions: \(x = \frac{D_x}{D}\) and \(y = \frac{D_y}{D}\)

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Cramer's Rule

Cramer's Rule is a method for solving systems of linear equations using determinants. It applies to systems with the same number of equations and unknowns, where the solution for each variable is found by replacing the corresponding column of the coefficient matrix with the constants vector and dividing by the determinant of the coefficient matrix.
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Determinants of 2x2 Matrices

The determinant of a 2x2 matrix [[a, b], [c, d]] is calculated as ad - bc. This value is crucial in Cramer's Rule, as it determines whether the system has a unique solution (non-zero determinant) or not. Calculating determinants accurately is essential for applying Cramer's Rule.
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Determinants of 2×2 Matrices

Systems of Linear Equations

A system of linear equations consists of two or more linear equations with the same variables. Understanding how to represent and manipulate these systems, such as writing them in matrix form, is fundamental for applying methods like Cramer's Rule to find solutions.
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Introduction to Systems of Linear Equations