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Ch. 5 - Systems and Matrices
Lial - College Algebra 13th Edition
Lial13th EditionCollege AlgebraISBN: 9780136881063Not the one you use?Change textbook
All textbooksLial 13th EditionCh. 5 - Systems and MatricesProblem 69
Chapter 6, Problem 69

Use Cramer's rule to solve each system of equations. If D = 0, then use another method to determine the solution set. See Examples 5–7. 1.5
x + 3y = 5
2x + 4y = 3

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1
Write the system of equations in standard form: \(1.5x + 3y = 5\) \(2x + 4y = 3\).
Identify the coefficients to form the coefficient matrix \(A\): \(A = \begin{bmatrix} 1.5 & 3 \\ 2 & 4 \end{bmatrix}\).
Calculate the determinant \(D\) of matrix \(A\) using the formula: \(D = (1.5)(4) - (3)(2)\).
If \(D \neq 0\), find the determinants \(D_x\) and \(D_y\) by replacing the respective columns of \(A\) with the constants vector \(\begin{bmatrix} 5 \\ 3 \end{bmatrix}\): \(D_x = \begin{vmatrix} 5 & 3 \\ 3 & 4 \end{vmatrix}\), \(D_y = \begin{vmatrix} 1.5 & 5 \\ 2 & 3 \end{vmatrix}\).
Use Cramer's rule to solve for \(x\) and \(y\): \(x = \frac{D_x}{D}\), \(y = \frac{D_y}{D}\). If \(D = 0\), then use another method such as substitution or elimination to find the solution set.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cramer's Rule

Cramer's Rule is a method for solving systems of linear equations using determinants. It applies when the system has the same number of equations as unknowns and the determinant of the coefficient matrix (D) is nonzero. The solution for each variable is found by replacing the corresponding column in the coefficient matrix with the constants from the equations and calculating the determinant.
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Determinant of a Matrix

The determinant is a scalar value that can be computed from a square matrix and provides important information about the matrix, such as invertibility. For a 2x2 matrix, the determinant is calculated as ad - bc. If the determinant is zero, the matrix is singular, meaning the system may have no solution or infinitely many solutions.
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Alternative Methods for Solving Systems

When the determinant D equals zero, Cramer's Rule cannot be used. Alternative methods include substitution, elimination, or using matrix row operations to find the solution set. These methods help determine whether the system has no solution, one solution, or infinitely many solutions.
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Related Practice
Textbook Question

Solve each system. (Hint: In Exercises 69–72, let 1/x = t and 1/y = u.)

2/x + 1/y = 3/2

3/x - 1/y = 1

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Textbook Question

Given A=[4−231],B=[510−237]A = \(\left\)[ \(\begin{matrix}\) 4 & -2 \\ 3 & 1 \(\end{matrix}\) \(\right\)], \(\quad\) B = \(\left\)[ \(\begin{matrix}\) 5 & 1 \\ 0 & -2 \\ 3 & 7 \(\end{matrix}\) \(\right\)] and C=[−541036]C = \(\left\)[ \(\begin{matrix}\) -5 & 4 & 1 \\ 0 & 3 & 6 \(\end{matrix}\) \(\right\)], find each product, if possible. See Examples 5–7. BA

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Textbook Question

Solve each problem. Find the radius and height (to the nearest thousandth) of an open-ended cylinder with volume 50 in.3 and lateral surface area 65 in.2.

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Textbook Question

Use Cramer's rule to solve each system of equations. If D = 0, then use another method to determine the solution set. See Examples 5–7.

5x+4y=105x + 4y = 10

5x+4y=105x + 4y = 10

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Textbook Question

Find each product, if possible.

[−2−3−42−104−23][01412−132−2]\(\left\)[ \(\begin{matrix}\) -2 & -3 & -4 \\ 2 & -1 & 0 \\ 4 & -2 & 3 \(\end{matrix}\) \(\right\)] \(\left\)[ \(\begin{matrix}\) 0 & 1 & 4 \\ 1 & 2 & -1 \\ 3 & 2 & -2 \(\end{matrix}\) \(\right\)]

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Textbook Question

Solve each problem. The supply and demand equations for a certain commodity are given. supply: p = 2000/(2000 - q) and demand: p = (7000 - 3q)/2q.

Find the equilibrium demand.

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