# Which System is Represented by the Graph

Which System is Represented by the Graph.

### Learning Outcomes

• Graph systems of equations
• Graph a organization of two linear equations
• Graph a system of two linear inequalities
• Evaluate ordered pairs as solutions to systems
• Determine whether an ordered pair is a solution to a organization of linear equations
• Make up one’s mind whether an ordered pair is a solution to a system of linear inequalities
• Classify solutions to systems
• Place what blazon of solution a organisation volition have based on its graph

The way a river flows depends on many variables including how big the river is, how much water it contains, what sorts of things are floating in the river, whether or non it is raining, and and so forth. If you want to best describe its menstruation, you lot must take into business relationship these other variables. A organisation of linear equations can help with that.

A
system of linear equations
consists of two or more linear equations made up of two or more variables such that all equations in the system are considered simultaneously. Yous will find systems of equations in every awarding of mathematics. They are a useful tool for discovering and describing how behaviors or processes are interrelated. It is rare to discover, for instance, a pattern of traffic period that that is just afflicted past weather. Accidents, fourth dimension of twenty-four hour period, and major sporting events are only a few of the other variables that tin can bear upon the flow of traffic in a city. In this section, nosotros will explore some basic principles for graphing and describing the intersection of ii lines that brand up a arrangement of equations.

## Graph a system of linear equations

In this section, we will look at systems of linear equations and inequalities in two variables.  Commencement, nosotros volition practice graphing two equations on the same gear up of axes, and and so nosotros will explore the different considerations y’all need to make when graphing two linear inequalities on the same fix of axes. The same techniques are used to graph a organization of linear equations equally you have used to graph single linear equations. Nosotros tin can utilize tables of values, slope and
y-intercept, or
x– and
y-intercepts to graph both lines on the aforementioned set of axes.

For example, consider the following system of linear equations in two variables.

$\begin{array}{r}2x+y=-eight\\ ten-y=-1\end{array}$

Permit’south graph these using gradient-intercept form on the aforementioned set of axes. Recall that gradient-intercept form looks like $y=mx+b$,  and then we will want to solve both equations for $y$.

First, solve for y in $2x+y=-8$ $\brainstorm{array}{c}2x+y=-8\\ y=-2x – viii\cease{array}$

2nd, solve for y in $x-y=-ane$ $\begin{array}{r}x-y=-ane\,\,\,\,\,\\ y=x+ane\finish{array}$

The system is at present written as

$\brainstorm{array}{c}y=-2x – 8\\y=x+1\end{array}$

Now y’all can graph both equations using their slopes and intercepts on the aforementioned set of axes, as seen in the figure below. Note how the graphs share one betoken in common. This is their point of intersection, a point that lies on both of the lines.  In the adjacent section we will verify that this point is a solution to the system.

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In the following instance, y’all volition be given a organisation to graph that consists of ii parallel lines.

### Instance

Graph the system $\brainstorm{array}{c}y=2x+1\\y=2x-three\terminate{array}$ using the slopes and y-intercepts of the lines.

In the next example, you lot will be given a arrangement whose equations look different, only later graphing, turn out to be the aforementioned line.

### Example

Graph the organisation $\begin{assortment}{c}y=\frac{1}{2}ten+2\\2y-ten=iv\end{assortment}$ using the x – and y-intercepts.

Graphing a system of linear equations consists of choosing which graphing method you want to utilise and drawing the graphs of both equations on the aforementioned set up of axes. When you lot graph a system of linear inequalities on the same set of axes, in that location are a few more things you volition need to consider.

## Graph a system of 2 inequalities

Call up from the module on graphing that the graph of a unmarried linear inequality splits the
coordinate plane
into ii regions. On ane side lie all the solutions to the inequality. On the other side, there are no solutions. Consider the graph of the inequality $y<2x+five$.

The dashed line is $y=2x+5$. Every ordered pair in the shaded area below the line is a solution to $y<2x+5$, as all of the points below the line will make the inequality true. If you doubt that, effort substituting the
ten
and
y
coordinates of Points A and B into the inequality—yous’ll see that they work. So, the shaded area shows all of the solutions for this inequality.

The boundary line divides the coordinate aeroplane in half. In this example, it is shown as a dashed line every bit the points on the line don’t satisfy the inequality. If the inequality had been $y\leq2x+5$, then the boundary line would accept been solid.

Let’southward graph some other inequality: $y>−x$. You can check a couple of points to determine which side of the boundary line to shade. Checking points M and N yield true statements. So, we shade the area above the line. The line is dashed as points on the line are not true.

To create a system of inequalities, you need to graph ii or more inequalities together. Let’s employ $y<2x+5$ and $y>−x$ since we accept already graphed each of them.

The royal area shows where the solutions of the ii inequalities overlap. This surface area is the solution to the
system of inequalities. Any point within this imperial region will exist true for both $y>−x$ and $y<2x+five$.

In the next example, you lot are given a system of two inequalities whose purlieus lines are parallel to each other.

### Examples

Graph the system $\brainstorm{assortment}{c}y\ge2x+1\\y\lt2x-3\cease{assortment}$

In the adjacent section, we will come across that points can be solutions to systems of equations and inequalities.  We will verify algebraically whether a point is a solution to a linear equation or inequality.

## Determine whether an ordered pair is a solution for a arrangement of linear equations

The lines in the graph above are defined as

$\brainstorm{array}{r}2x+y=-eight\\ x-y=-1\end{assortment}$.

They cross at what appears to be $\left(-3,-two\right)$.

Using algebra, we tin can verify that this shared betoken is actually $\left(-3,-two\right)$ and non $\left(-2.999,-ane.999\right)$. By substituting the
x– and
y-values of the ordered pair into the equation of each line, you tin exam whether the betoken is on both lines. If the exchange results in a true statement, then you have plant a solution to the system of equations!

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Since the solution of the system must be a solution to
all
the equations in the arrangement, you volition demand to check the point in each equation. In the following example, we volition substitute -3 for
x
and -ii for
y
in each equation to test whether it is actually the solution.

### Example

Is $\left(-3,-ii\right)$ a solution of the organisation

$\begin{assortment}{r}2x+y=-8\\ x-y=-i\end{array}$

### Instance

Is (iii, nine) a solution of the system

$\begin{array}{r}y=3x\\2x–y=half-dozen\finish{array}$

Is $(−2,4)$ a solution for the system

$\begin{array}{r}y=2x\\3x+2y=1\finish{assortment}$

Before you do any calculations, look at the indicate given and the first equation in the system.  Can you predict the answer to the question without doing whatsoever algebra?

Remember that in order to be a solution to the organisation of equations, the values of the point must be a solution for both equations. Once yous discover i equation for which the bespeak is imitation, yous have determined that it is not a solution for the system.

Nosotros can use the same method to determine whether a point is a solution to a system of linear inequalities.

## Make up one’s mind whether an ordered pair is a solution to a system of linear inequalities

On the graph above, you can see that the points B and N are solutions for the system because their coordinates volition make both inequalities true statements.

In contrast, points K and A both prevarication outside the solution region (purple). While betoken M is a solution for the inequality $y>−10$ and bespeak A is a solution for the inequality $y<2x+5$, neither signal is a solution for the
system. The following example shows how to examination a point to see whether it is a solution to a system of inequalities.

### Example

Is the point (2, ane) a solution of the system $x+y>1$ and $2x+y<8$?

Here is a graph of the organization in the example higher up. Discover that (2, 1) lies in the majestic area, which is the overlapping expanse for the two inequalities.

### Example

Is the betoken (2, i) a solution of the organisation $x+y>one$ and $3x+y<4$?

Here is a graph of this system. Notice that (2, 1) is not in the majestic area, which is the overlapping expanse; it is a solution for i inequality (the ruby region), but it is not a solution for the second inequality (the blue region).

As shown above, finding the solutions of a system of inequalities can be done past graphing each inequality and identifying the region they share. Below, you lot are given more than examples that show the entire process of defining the region of solutions on a graph for a arrangement of two linear inequalities.  The full general steps are outlined below:

• Graph each inequality every bit a line and determine whether it will be solid or dashed
• Make up one’s mind which side of each boundary line represents solutions to the inequality past testing a betoken on each side
• Shade the region that represents solutions for both inequalities

In this department nosotros have seen that solutions to systems of linear equations and inequalities can be ordered pairs. In the next section, nosotros will work with systems that accept no solutions or infinitely many solutions.

## Utilise a graph to classify solutions to systems

Recall that a linear equation graphs every bit a line, which indicates that all of the points on the line are solutions to that linear equation. There are an infinite number of solutions. As we saw in the last department, if you have a system of linear equations that intersect at one point, this point is a solution to the system.  What happens if the lines never cross, as in the instance of parallel lines?  How would yous depict the solutions to that kind of system? In this section, we will explore the three possible outcomes for solutions to a system of linear equations.

### Three possible outcomes for solutions to systems of equations

Recall that the solution for a arrangement of equations is the value or values that are true for
all
equations in the organisation. There are three possible outcomes for solutions to systems of linear equations.  The graphs of equations within a organization can tell y’all how many solutions exist for that system. Expect at the images below. Each shows ii lines that make up a organisation of equations.

I Solution No Solutions Infinite Solutions
If the graphs of the equations intersect, and so there is one solution that is true for both equations. If the graphs of the equations exercise not intersect (for example, if they are parallel), so there are no solutions that are true for both equations. If the graphs of the equations are the same, then at that place are an infinite number of solutions that are true for both equations.
• One Solution: When a arrangement of equations intersects at an ordered pair, the organization has one solution.
• Infinite Solutions:
Sometimes the two equations will graph as the aforementioned line, in which instance we have an infinite number of solutions.
• No Solution:
When the lines that brand up a system are parallel, there are no solutions because the two lines share no points in common.

### Instance

Using the graph of $\begin{array}{r}y=x\\x+2y=half dozen\end{array}$, shown beneath, determine how many solutions the system has.

Using the graph of $\begin{array}{r}y=3.5x+0.25\\14x–4y=-4.5\end{assortment}$, shown below, determine how many solutions the system has.

### Example

How many solutions does the system $\begin{array}{r}y=2x+1\\−4x+2y=2\end{array}$ accept?

In the side by side section, we volition learn some algebraic methods for finding solutions to systems of equations.  Recall that linear equations in one variable can have i solution, no solution, or many solutions and we can verify this algebraically.  Nosotros will use the same ideas to allocate solutions to systems in ii variables algebraically.

## Which System is Represented by the Graph

Source: https://courses.lumenlearning.com/beginalgebra/chapter/introduction-to-systems-of-linear-equations/

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