Solving a system of equations
using substitution
You are going to
x
–
y
=
7
substitute the
information in the x = 17 – 4y
box into the
(17
–
4y)
–
y
=
7
other equation
and solve.
17 – 5y = 7
What we know now
is that the answer
will be (?, 2)
-17
-17
– 5y = -10
-5
-5
y=2
To find the x part of our
coordinate, we will go back to
our equation with the box and
substitute
x = 17 – 4(2)
x = 17 – 8
x=9
Now that
we’ve
Substituted
we know
The
complete
answer
Is (9, 2)
You are going to
2x – y = 5
substitute the
x=y+3
information in the
2(y + 3) – y = 5
box into the
2y + 6 – y = 5
other equation
and solve.
y+6=5
What we know now
is that the answer
will be (?, -1)
-6 -6
y= -1
To find the x part of our
coordinate, we will go back to
our equation with the box and
substitute
x = -1 + 3
x=2
Now that
we’ve
Substituted
we know
The
complete
answer
Is (2, -1)
You are going to -5x + 3y = 51
substitute the
y = 10x – 8
information in
the box into the-5x + 3(10x – 8) = 51
other equation -5x + 30x – 24 = 51
and solve.
25x – 24 = 51
What we know now
is that the answer
will be (3, ?)
+24 +24
25x = 75
25 25
x=3
To find the y part of our
coordinate, we will go back to
our equation with the box and
substitute
y = 10(3) – 8
y = 30 – 8
y = 22
Now that
we’ve
Substituted
we know
The
complete
answer
Is (3, 22)
y = -2x + 9
4x – y = -15
4x – (-2x + 9)= -15
4x + 2x – 9 = -15
6x – 9 = -15
+9
+9
What we know now
6x = -6
is that the answer
6 6
will be (-1, ?)
x = -1
You are going to
substitute the
information in
the box into the
other equation
and solve.
To find the y part of our
coordinate, we will go back to
our equation with the box and
substitute
y = -2(-1) + 9
y=2+9
y = 11
Now that
we’ve
Substituted
we know
The
complete
answer
Is (-1, 11)
Pg. 439
4 – 20 even