In Example 3, change the coefficient of x² in the first equation from 2 to 1 and then solve the system.

Data from Example 3

By addition or subtraction, solve the system of equations

We note that if we add the corresponding sides of each equation, y² is eliminated. This leads to the solution.

For x = 2, we have two corresponding y-values, y = ±1. Also, for x = −2, we have two corresponding y-values, y = ±1. Thus, we have four solutions:

Each solution checks in the original equations. The graphical solutions are shown in Fig. 14.11.

2x + y = 9 x - y = 3