System of Linear Equations: Substitution Method

System of Linear Equations: Substitution Method

How to solve system of linear equations problems by using the substitution method: example and its solutions. (2 ways)

Example

Solve the system of equations. x - y = 4, 2x + y = 5

Choose one of the equations
and change it to 'x = ' or 'y = '.

Let's choose x - y = 4
and change it to x = y + 4.

Put y + 4 into the other equation's x.
Then y = -1.

Put y = -1 into x = y + 4.
Then x = 3.

So the answer is x = 3, y = -1.

Example: Another Solution

Solve the system of equations. x - y = 4, 2x + y = 5

Let's solve the same example
by choosing the other equation.

Let's choose 2x + y = 5
and change it to y = -2x + 5.

Put -2x + 5 into the other equation's y.
Then x = 3.

Put x = 3 into y = -2x + 5.
Then y = -1.

So the answer is x = 3, y = -1.

As you can see, you got the same answer.