Solve a system of equations using substitution

Use substitution when one equation is easy to isolate.

Lesson 3

Concept

Solve one equation for a variable, substitute into the other equation, then back-substitute to find both values.

Solve y = 2x + 1 and x + y = 10.

Best first step for y = 3x - 2 and x + y = 6 is:

Eliminate immediately

Substitute y into second equation

Graph only

Add equations unchanged

After finding x in substitution, you must:

Stop

Back-substitute to find y

Multiply both equations by 0

Only graph

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

1.Back-substitute and verify

2.Solve for one variable

3.Substitute into other equation

4.Isolate a variable

When is substitution more efficient than elimination?