Solve a system of equations using elimination

Eliminate one variable by combining equations strategically.

Lesson 5

Concept

Multiply equations when needed so one variable has opposite coefficients, then add/subtract to eliminate it.

Solve 2x + y = 9 and 2x - y = 3.

In elimination, why multiply an equation first?

To change solution set

To create opposite coefficients

To remove constants

To force graphing

After elimination gives x, what next?

Guess y

Back-substitute for y

Restart

Ignore y

These steps are out of order — can you fix them?

1.Align equations

2.Add/subtract to eliminate

3.Back-substitute and verify

4.Create opposite coefficients

What is a common elimination mistake?