Algebra and Pre-Algebra Lessons

Algebra 1 | Pre-Algebra | Practice Tests | Algebra Readiness Test

Algebra E-Course and Homework Information

Algebra E-course Info | Log In to Algebra E-course | Homework Calculator

Formulas and Cheat Sheets

Formulas | Algebra Cheat Sheets

Using the Substitution Method

Use Substitution to solve the system of equations

4x + y = 0
2y + x = -7

Comments for Using the Substitution Method

Average Rating starstarstarstarstar

Click here to add your own comments

Jan 17, 2011
Using the Substitution Method
by: Karin

In order to use the Substitution Method, you must first solve one of the equations for one variable. This means that you must rewrite one of the equations as x = ... or y=...

It's easiest to solve equation 1 for y.

1. 4x+y = 0
2. 2y+x = -7

Step 1: Solve equation 1 for y by subtracting 4x from both sides.

4x-4x + y = 0-4x

y = -4x

Now that we know what y is equal to (-4x), we can substitute this into the 2nd equation.

2(-4x) +x = -7

-8x +x = -7

Simplify further by combining x terms:

-7x = -7

Divide by -7 to isolate the variable.

-7x/-7 = -7/-7

x = 1

We now know that x is equal to 1, so we can substitute this for x and solve for y. I will use the new equation that I wrote: y = -4x

y = -4(1)
y = -4

Our solution is: (1, -4)

I hope this helps!


Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Students.

Like This Page?

Top of the Page

Connect and Follow Algebra Class

Copyright © 2009-2015 Karin Hutchinson ALL RIGHTS RESERVED