Warm Up
Solve using substitution.
1. y = 2x –1
and 2x + y = 3
2. x = y + 3
and 2x – y = 5
3. y = -6x – 2 and
12x + 2y = -6
Answers
1. (1, 1)
2. (2, -1)
3. No solution
Lesson 7.3B
Solving systems of equations using
substitution
5 Simple Steps To finding the
Solution:
Solve one equation for either x or y
Substitute the expression into the other
equation
Solve for the variable
Substitute the value back in and solve
Check your answer, is it a solution?
Remember that a point consists of an “x” value and a
“y” value. You have to find BOTH to find the solution!
S’more Practice…
Solve the following system of equations.
1. 2x + y = 12
Hint:
y + 3x = 23
You must pick
one equation
to solve for a
single variable
so that you
can substitute
it into the
other
equation!
(11, -10)
Example 2: -6x – 8y = 4
6x + 6y = -6
(-2, 1)
Example 3: 2x + 2y = -16
4x – 4y = 32
(0, -8)
Class Activity:
Substitution Revolution!
Your teacher will pass out a note card to each of you.
Once you have your note card, write down an
equation in 2 variables (Ex. y =-3x +9). The equation
can be anything you want, but please keep the
numbers in front of the variables between -6 and 6.
When everyone has their equation break into 2 lines
and begin substituting with the person across from you
(this means everyone should have a sheet of lined
paper out to show your work and turn into your
teacher at the end of class). Once everyone is done
solving the revolution begins…and you will substitute
your equation with the next person across from you!
Summary:
Explain why it is important to keep the
expression you substitute into the other
equation wrapped in parentheses.
Homework:
Worksheet 7.3B