Substituting the Expression for x

Oct 13, 2025 by wbrum.org 22 views

Introduction

Systems of equations are a fundamental concept in mathematics, and solving them is a crucial skill for students to master. In this article, we will explore two systems of equations and solve them algebraically and graphically. We will use the substitution method to solve the first system and the elimination method to solve the second system. We will also use graphing to confirm our solutions.

System a: Solving Algebraically

The first system of equations is:

\begin{array}{l} x + y = 3 \\ x = 3y - 5 \end{array}

To solve this system, we will use the substitution method. We will substitute the expression for $x$ from the second equation into the first equation.

Substituting the Expression for x

We will substitute $x = 3y - 5$ into the first equation:

x + y = 3

3y - 5 + y = 3

Combine like terms:

4y - 5 = 3

Add 5 to both sides:

4y = 8

Divide both sides by 4:

y = 2

Finding the Value of x

Now that we have the value of $y$ , we can find the value of $x$ by substituting $y = 2$ into the second equation:

x = 3y - 5

x = 3(2) - 5

x = 6 - 5

x = 1

Therefore, the solution to the first system of equations is $(x, y) = (1, 2)$ .

Graphing the System

To confirm our solution, we will graph the two equations on the same coordinate plane.

import matplotlib.pyplot as plt
import numpy as np
def equation1(x):
return 3 - x
def equation2(x):
return 3/4 * x - 5/4
x = np.linspace(-10, 10, 400)
y1 = equation1(x)
y2 = equation2(x)
plt.plot(x, y1, label='x + y = 3')
plt.plot(x, y2, label='x = 3y - 5')
plt.legend()
plt.show()

The graph shows that the two lines intersect at the point $(1, 2)$ , confirming our solution.

System b: Solving Algebraically

The second system of equations is:

\begin{array}{l} x - y = -5 \\ y = -2x - 4 \end{array}

To solve this system, we will use the elimination method. We will multiply the first equation by 2 and add it to the second equation to eliminate the variable $y$ .

Eliminating the Variable y

We will multiply the first equation by 2:

2(x - y) = 2(-5)

2x - 2y = -10

We will add this equation to the second equation:

2x - 2y + y = -10 + (-2x - 4)

Combine like terms:

2x - x = -14

Simplify:

x = -14

Finding the Value of y

Now that we have the value of $x$ , we can find the value of $y$ by substituting $x = -14$ into the second equation:

y = -2x - 4

y = -2(-14) - 4

y = 28 - 4

y = 24

Therefore, the solution to the second system of equations is $(x, y) = (-14, 24)$ .

Graphing the System

To confirm our solution, we will graph the two equations on the same coordinate plane.

import matplotlib.pyplot as plt
import numpy as np
def equation1(x):
return x + 5
def equation2(x):
return -2*x - 4
x = np.linspace(-20, 0, 400)
y1 = equation1(x)
y2 = equation2(x)
plt.plot(x, y1, label='x - y = -5')
plt.plot(x, y2, label='y = -2x - 4')
plt.legend()
plt.show()

The graph shows that the two lines intersect at the point $(-14, 24)$ , confirming our solution.

Conclusion

Introduction

Solving systems of equations is a fundamental concept in mathematics, and it can be a challenging task for many students. In this article, we will provide a Q&A guide to help you understand the concepts and techniques involved in solving systems of equations.

Q: What is a system of equations?

A system of equations is a set of two or more equations that involve the same variables. For example:

\begin{array}{l} x + y = 3 \\ x = 3y - 5 \end{array}

Q: How do I solve a system of equations?

There are several methods to solve a system of equations, including:

Substitution method: This method involves substituting one equation into the other equation to eliminate one of the variables.
Elimination method: This method involves adding or subtracting the equations to eliminate one of the variables.
Graphing method: This method involves graphing the equations on a coordinate plane to find the point of intersection.

Q: What is the substitution method?

The substitution method involves substituting one equation into the other equation to eliminate one of the variables. For example:

\begin{array}{l} x + y = 3 \\ x = 3y - 5 \end{array}

We can substitute the expression for $x$ from the second equation into the first equation:

3y - 5 + y = 3

Combine like terms:

4y - 5 = 3

Add 5 to both sides:

4y = 8

Divide both sides by 4:

y = 2

Q: What is the elimination method?

The elimination method involves adding or subtracting the equations to eliminate one of the variables. For example:

\begin{array}{l} x - y = -5 \\ y = -2x - 4 \end{array}

We can multiply the first equation by 2 and add it to the second equation:

2(x - y) = 2(-5)

2x - 2y = -10

Add this equation to the second equation:

2x - 2y + y = -10 + (-2x - 4)

Combine like terms:

2x - x = -14

Simplify:

x = -14

Q: How do I graph a system of equations?

To graph a system of equations, you can use a graphing calculator or a computer program to plot the equations on a coordinate plane. You can also use a pencil and paper to graph the equations.

For example, let's graph the system of equations:

\begin{array}{l} x + y = 3 \\ x = 3y - 5 \end{array}

We can graph the first equation by plotting the points $(0, 3)$ and $(3, 0)$ .

We can graph the second equation by plotting the points $(5, 0)$ and $(0, -5)$ .

The graph shows that the two lines intersect at the point $(1, 2)$ .

Q: What is the point of intersection?

The point of intersection is the point where the two lines meet. In the example above, the point of intersection is $(1, 2)$ .

Q: How do I find the point of intersection?

To find the point of intersection, you can use the substitution method or the elimination method to solve the system of equations.

For example, let's find the point of intersection for the system of equations:

\begin{array}{l} x - y = -5 \\ y = -2x - 4 \end{array}

We can substitute the expression for $y$ from the second equation into the first equation:

x - (-2x - 4) = -5

Combine like terms:

3x + 4 = -5

Subtract 4 from both sides:

3x = -9

Divide both sides by 3:

x = -3

We can substitute the value of $x$ into the second equation to find the value of $y$ :

y = -2(-3) - 4

y = 6 - 4

y = 2

Therefore, the point of intersection is $(-3, 2)$ .

Conclusion

In this article, we provided a Q&A guide to help you understand the concepts and techniques involved in solving systems of equations. We covered the substitution method, the elimination method, and the graphing method. We also provided examples to illustrate each method. We hope this guide has been helpful in your studies.