Question

Use the graph-and-check method to solve the system of linear equations. $$ \begin{aligned} &y=-2 x+3\\\ &y=x-3 \end{aligned} $$

Short answer

The intersection point of the two lines provides the solution to the system of equations. If the lines intersect at a single point, the system has one solution represented by that point. If the lines are parallel (and thus never intersect), the system has no solutions. If the two lines coincide, the system has infinitely many solutions.

Step-by-step solution

Sketch the First Equation

Begin by plotting the graph of the first equation, \(y=-2x+3\). This equation is in the slope-intercept form \(y=mx+b\), where m is the slope and b is the y-intercept. The graph is a straight line with a slope of -2 and y-intercept 3.

Sketch the Second Equation

Next, draw the graph of the second equation, \(y=x-3\). This equation is also in the slope-intercept form. Thus, it is a straight line with a slope of 1 and y-intercept -3.

Identify the Intersection Point

Looking at the plot, identify the point where the two lines intersect. This point provides the x and y values that satisfy both equations, thus solving the system of equations.

Key concepts

Graph-and-Check Method

The graph-and-check method is a visual approach to solving systems of linear equations. It involves drawing the graph of each equation on the same set of axes and then finding the point at which they intersect.

Step-by-step, one would plot the lines by determining the y-intercept and slope for each equation. In the provided exercise, this method starts by graphing the equation \(y = -2x + 3\). This line crosses the y-axis at 3, known as the y-intercept. We can then use the slope, which is -2, to determine the direction and steepness of the line. You proceed by plotting a point for every two units down and one across.

Next, you draw the graph of the second equation, \(y = x - 3\), which crosses the y-axis at -3. The slope is 1, indicating a line that rises one unit for every unit it moves to the right. By plotting these on the same graph paper, you can visually determine the point where the two lines cross; this intersection represents the solution to the system.

The 'check' part of the method refers to substituting the coordinates of the intersection point back into the original equations to verify that the point satisfies both equations.

Slope-Intercept Form

The slope-intercept form of a linear equation is given by \(y = mx + b\), where \(m\) is the slope and \(b\) is the y-intercept of the line. The y-intercept is the point where the line crosses the y-axis, and the slope represents the tilt of the line on the graph.

In this form, plotting a line becomes straightforward because it provides clear starting points, the slope and the y-intercept. For example, with \(y = -2x + 3\), the y-intercept \(b\) is 3, which means you start at the point (0, 3) on the graph. The slope \(m\) is -2, indicating the line will fall as it moves to the right, specifically two units down for every one unit right.

When given a problem, it's often useful to convert equations into the slope-intercept form. Doing so simplifies the process of graphing and understanding the relationship between the equations. This method provides an immediate visual representation that can help pinpoint a solution.

Linear Equations Intersection

The intersection of linear equations refers to the point where two or more lines on a graph cross each other. When you're given a system of linear equations, finding this intersection point is crucial because it represents the solution where all the equations in the system are satisfied simultaneously.

Each line on the graph of a linear equation represents all the points (x, y) that satisfy the equation. Thus, the intersection represents the specific (x, y) pair that is true for all equations involved. In our example, the lines represented by \(y = -2x + 3\) and \(y = x - 3\) intersect at a single point. The coordinates of this point are the x and y values you are solving for in the system of equations.

If you are working with the graph-and-check method, the visual intersection provides an immediate solution, which should still be verified algebraically by substituting the intersection coordinates into the original equations. Remember, not all systems have a single solution; some can have infinitely many solutions or none at all, scenarios that occur when lines coincide or are parallel, respectively.