Unit 2, Lesson 14
Solving Systems by Elimination (Part 1)
Algebra 1
14.1
Warm-up
Notice and Wonder: Hanger Diagrams
What do you notice? What do you wonder?
Sign in to view assessments and invite other educators
Sign in using your existing Kendall Hunt account. If you don’t have one, create an educator account.
What do you notice? What do you wonder?
Another way to solve systems of equations algebraically is by elimination. Just like in substitution, the idea is to eliminate one variable so that we can solve for the other. This is done by adding or subtracting equations in the system. Let’s look at an example.
Notice that one equation has
If we add the second equation to the first, the
Now that we know
In this system, the coefficient of
What if the equations don't have opposite coefficients for the same variable, like in the following system?
Notice that both equations have
Substituting 5 for
Adding or subtracting the equations in a system creates a new equation. How do we know the new equation shares a solution with the original system?
If we graph the original equations in the system and the new equation, we can see that all three lines intersect at the same point, but why do they?
Three intersecting lines on coordinate plane, origin O. X axis from negative 4 to 14 by 2’s. Y axis from negative 4 to 12 by 2’s. Black line through negative 4 comma 12 and 10 comma 2. Blue line passes through negative 4 comma 1 and 10 comma 2. Red vertical line passes through 10 comma 2. All lines intersect at 10 comma 2.
In future lessons, we will investigate why this strategy works.
Elimination is a method of solving a system of two equations in two variables. A multiple of one equation is added to or subtracted from another to get an equation with only one of the variables. (The other variable is eliminated.)