Download Steps for Substitution - Brookwood High School

1.3 Solving Systems by
Substitution
Steps for Substitution
1.Solve for the “easiest” variable
2.Substitute this expression into the
other equation
3.Solve for remaining variable
4.Substitute the value into the starting
equation to solve for final variable
5.Write as ordered pair and check
Solve by
Substitution
3X + Y = 8
18X + 2Y = 4
Show me how to solve by
Substitution!!
X=Y+3
2X + 2Y = 2
Steps for Elimination
1. Line up the equations.
2. Look to see if you add the “columns” if either
variable is eliminated.
3. If it isn’t, look to see what you could multiply by
to eliminate a variable.
4. Rewrite the equation you need to multiply and
multiply the whole equation by that number.
5. Rewrite the other equation under it.
6. Add the “columns.”
7. Solve for that variable.
8. Substitute that answer into one of the original
equations and solve for the other variable.
9. Write it as an ordered pair.
Solve by
2X + Y = 8
X – Y = 10
Elimination
Solve by
3X + Y = 8
18X + 2Y = 4
Elimination
Solve by
X+Y=4
2X + 3Y = 9
Elimination
Solve by
2X – 4Y = 5
–X + 2Y = 8
Elimination
Solve by
4Y + 30 = 10X
5X – 2Y = 15
Elimination
– 4.5x + 7.5Y = – 9
3x – 5Y = 6
Multiply by ten to eliminate decimals.
– 45X+ 75 Y= – 90
3X – 5Y = 6
1
7y  x  2
2
2y  x  4
2x – 3y + 4z = 8
3x + 2y = 7
x=1
What size is the
system?
Let’s look at Page 15 # 22
Take the words and build a system of equations.
Assignment