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Determine whether each system of linear equations has (a) one and only one solution, (b) infinitely many solutions, or (c) no solution. Find all solutions whenever they exist. $$ \begin{array}{l} 3 x-4 y=7 \\ 9 x-12 y=14 \end{array} $$

Short Answer

Expert verified
The given system of linear equations has (c) no solution because when we attempt to eliminate a variable using the elimination method, we get a false statement, \(0 = -7\).

Step by step solution

01

Formulate the Equation for Elimination

To eliminate y, we can multiply the first equation by 3, so that the coefficient of y in both equations is the same, and then subtract the first equation from the second. $$ \begin{array}{l} (3)(3 x-4 y)=(3)7 \\\ \end{array} $$
02

Multiply Equation and Subtract

After multiplying the first equation by 3, we get: $$ \begin{array}{l} 9 x-12 y=21 \\\ 9 x-12 y=14 \end{array} $$ Now subtract the first equation from the second equation: $$ \begin{array}{l} (9 x-12 y)-(9 x - 12 y)=14 - 21 \\\ \end{array} $$
03

Evaluate the Resulting Equation and Determine Solution Type

Upon subtracting, we get: $$ \begin{array}{l} 0 =-7 \\\ \end{array} $$ The resulting equation is false. This means that the given system of linear equations has no solution. Therefore, the answer is (c) no solution.

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Key Concepts

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

One Solution
In the realm of linear algebra, a system of equations with one solution implies that the lines described by these equations intersect at a single point. This unique point of intersection is the only set of values that satisfy all equations simultaneously. The coordinates of this point simultaneously solve all the equations.

How can you confirm if a system has one solution? Well, if the equations are not multiples of each other and their slopes are different, they are likely to cross at one point. Such systems are known as independent systems and exhibit consistent behavior, meaning that there's definitely a solution to be found.
Infinitely Many Solutions
Moving to our next condition, when a system of equations has infinitely many solutions, it means that the equations represent the same line. That is, every single point on the line satisfies both equations, making them dependent systems.

An observation of this scenario reveals that the equations involved are just different forms of the same linear equation. Consequently, any point that lies on this line will solve the system, leading to an infinite set of solutions. In simpler terms, you could picture two lines lying directly on top of each other, perfectly aligned.
No Solution
In certain cases, a system of equations might lead us to a dead end, a situation where there is no solution. This typically occurs when the lines corresponding to the equations are parallel and never intersect. Just like two train tracks that run alongside each other indefinitely without ever meeting, these equations have the same slope but different y-intercepts.

A mathematical way to identify a 'no solution' circumstance would be when an attempt to solve the system results in a false statement, such as \(0=-7\). This indicates a contradiction, confirming that no set of x and y values will satisfy both equations simultaneously.
Elimination Method
Lastly, let's address a strategy used to solve these systems, called the elimination method. It's a procedure that combines equations in such a way that one variable gets eliminated, making it easier to solve for the remaining variable.

The elimination process often involves multiplying equations by certain factors to align the coefficients of a chosen variable. Once aligned, the equations can be subtracted from one another to cancel out the chosen variable. This method is particularly effective in systems where the variables are not already set up for easy elimination. After eliminating one variable, you're usually left with a simpler equation to solve for the other variable.

After the first variable is determined, it can be substituted back into one of the original equations to find the value of the second variable. The core of the method lies in simplifying complex systems into more manageable single-variable equations.

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Most popular questions from this chapter

Solve the system of linear equations using the Gauss-Jordan elimination method. $$ \begin{aligned} x_{1}-2 x_{2}+x_{3} &=6 \\ 2 x_{1}+x_{2}-3 x_{3} &=-3 \\ x_{1}-3 x_{2}+3 x_{3} &=10 \end{aligned} $$

Determine whether the statement is true or false. If it is true, explain why it is true. If it is false, give an example to show why it is false. If \(A^{-1}\) does not exist, then the system \(A X=B\) of \(n\) linear equations in \(n\) unknowns does not have a unique solution.

Let $$ \begin{array}{l} A=\left[\begin{array}{lll} 0 & 3 & 0 \\ 1 & 0 & 1 \\ 0 & 2 & 0 \end{array}\right] \quad B=\left[\begin{array}{rrr} 2 & 4 & 5 \\ 3 & -1 & -6 \\ 4 & 3 & 4 \end{array}\right] \\ C=\left[\begin{array}{rrr} 4 & 5 & 6 \\ 3 & -1 & -6 \\ 2 & 2 & 3 \end{array}\right] \end{array} $$ a. Compute \(A B\). b. Compute \(A C\). c. Using the results of parts (a) and (b), conclude that \(A B=A C\) does not imply that \(B=C\).

Three network consultants, Alan, Maria, and Steven, each received a year-end bonus of \(\$ 10,000\), which they decided to invest in a \(401(\mathrm{k})\) retirement plan sponsored by their employer. Under this plan, employees are allowed to place their investments in three funds: an equity index fund (I), a growth fund (II), and a global equity fund (III). The allocations of the investments (in dollars) of the three employees at the beginning of the year are summarized in the matrix $$ \begin{array}{l} \text { II }\\\ \begin{array}{c} \text { Alan } \\ A=\text { Maria } \\ \text { Steven } \end{array}\left[\begin{array}{lll} 4000 & 3000 & 3000 \\ 2000 & 5000 & 3000 \\ 2000 & 3000 & 5000 \end{array}\right] \end{array} $$ The returns of the three funds after 1 yr are given in the matrix $$ \begin{array}{r} \mathrm{I} \\ B=\mathrm{II} \\ \mathrm{III} \end{array}\left[\begin{array}{l} 0.18 \\ 0.24 \\ 0.12 \end{array}\right] $$ Which employee realized the best return on his or her investment for the year in question? The worst return?

The problems in exercise correspond to those in exercises 15-27, Section 2.1. Use the results of your previous work to help you solve these problems. Cantwell Associates, a real estate developer, is planning to build a new apartment complex consisting of one-bedroom units and two- and three-bedroom townhouses. A total of 192 units is planned, and the number of family units (two- and three-bedroom townhouses) will equal the number of one-bedroom units. If the number of one-bedroom units will be 3 times the number of threebedroom units, find how many units of each type will be in the complex.

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