Problem 31 - Algebra and Trigonometry

Question

Solve by the method of your choice. Identify systems with no solution and systems with infinitely many solutions, using set notation to express their solution sets. \(\left\\{\begin{array}{l}{x=9-2 y} \\ {x+2 y=13}\end{array}\right.\)

Step-by-Step Solution

Answer

The given system of equations has a unique solution (7, 1) which is represented as {(7, 1)} in set notation.

Step 1: Express Both Equations In Standard Form

In the standard form, equations should look like Ax + By = C. The given equations in standard form would be: \Equation 1: -2y + x = 9, \Equation 2: x + 2y = 13

Step 2: Solve for x and y

Equation 1 says that x = 9 + 2y and equation 2: x + 2y = 13. The two statements can be combined to solve for y, which leads to: 9 + 2y + 2y = 13. Simplifying that gives: 4y = 4. Hence, y = 1. Substitute y = 1 into either of the equations to find x. Choosing the first equation, we get: x = 9 - 2*1, leading to x = 7.

Step 3: Express the Solution in Set Notation

The solution is then (x, y) = (7, 1). In set notation, this can be expressed as: {(7, 1)}.

Key Concepts

Method of Substitution

The method of substitution is a powerful algebraic tool used to find the solutions to a system of equations. It involves rearranging one of the equations to isolate one variable and then substituting this expression into the other equation. This can simplify the system by reducing it to a single equation with one variable, which can subsequently be solved.

For example, consider a system with two equations: Equation 1: \(x = 9 - 2y\), and Equation 2: \(x + 2y = 13\). By expressing \(x\) from Equation 1 as \(9 - 2y\), you now have an expression that can be substituted for \(x\) in Equation 2. This substitution leads to \(9 - 2y + 2y = 13\), which simplifies to \(9 = 13\), solving for the single remaining variable.

• Isolate one variable from one of the equations.
• Substitute the expression obtained in the other equation.
• Solve for the remaining variable.
• Use the value of the resolved variable to find the value of the other variable by substitution.

When the substitution leads to a true statement, it confirms that the values found are indeed solutions to the system of equations. Substitution is especially useful when equations are already solved for a particular variable making the substitution straightforward.

Standard Form Linear Equations

Standard form linear equations are a way to uniformly express linear equations to simplify the process of solving them, especially when dealing with systems of equations. The standard form is represented as \(Ax + By = C\), where \(A\), \(B\), and \(C\) are constants, and \(x\) and \(y\) are variables.

Let's consider the system from the original exercise. The equations given in the problem are \(x = 9 - 2y\) and \(x + 2y = 13\). To put them into standard form, you would rewrite them as: Equation 1: \(-2y + x = 9\), and Equation 2: \(x + 2y = 13\), both of which now fit the \(Ax + By = C\) format.

The benefits of using standard form are:

• It provides a consistent structure for identifying and solving systems of equations.
• It enables the use of multiple methods of solution, such as substitution, elimination, or graphing.
• It makes it easier to compare equations and determine if they are parallel or the same line, which is useful in analyzing the system's solutions.

Practically, to convert any linear equation to standard form, you may need to rearrange terms, combine like terms, or multiply by a constant to clear fractions or decimals.

Set Notation

Set notation is a way of defining collections of objects, in our case, solutions to equations or systems of equations. It's a concise way to express complex relationships and solve mathematical problems. In terms of solutions to equations, set notation allows us to precisely state the condition of the solutions.

For instance, if a system has one solution, like the one with \(x = 7\) and \(y = 1\) from our original exercise, we can represent it as \({(7, 1)}\), which means there is a single ordered pair that is the solution to the system. If a system has no solution or infinitely many solutions, we use set notation to accurately describe these scenarios:

• A system with no solution can be represented by an empty set, \(\emptyset\), indicating there are no ordered pairs that satisfy both equations.
• A system with infinitely many solutions can be represented using a set with a general description of limitless pairs, such as \({(x, y) | x + y = k}\), where \(k\) is some constant, indicating that any pair \((x, y)\) that satisfies the equation is part of the solution set.

In summary, set notation simplifies the representation of solution sets, while also being precise and expressive for varying scenarios encountered with systems of equations.