A Pair of Linear Equations in Two Variables

The addition method always has the same steps

1. Move variables to the left and constants to the right

2. Select one of the variables

3. Modify the equations so that the coefficients for the selected variable are opposite numbers.

4. Add the equations together

5. Solve the remaining variable

6. Place the resolved variable into one of the original equations

Example 1

Solve a pair of linear equations using the addition method.

Let's choose y and multiply the lower equation by 2

We substitute x = 4 into the first equation

The solution to a pair of linear equations in two variables is x = 4 and y = 2

We can also solve either variable from one equation and then substitute it into the other equation.

Example 2

Solve variable y from the first equation

Now we can substitute it into the other equation and solve x

And so the variable for y is

The solution is x = 2 and y = 3

We can also solve Example 2 by drawing graphs

The graphs are straight lines and the solution to a pair of linear equations is the intersection of these lines (2,3), i.e. x = 2 and y = 3.

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