6.2 Solving Systems by Substitution

Objectives:

1. Solve systems of linear equations in two variables by substitution.

Example 1: Solve for x when – A. B.

C.

D.

Why is graphing not always the most useful way to solve a system of equations?

We don’t always land on whole numbers!

Remember – when solving a system of linear equations we are looking for an ordered pair that makes both equations true.

We will use substitution when:

1. Both equations are solved for 1 variable.

2. 1 equation is solved for a variable, and one is in standard form.

Example 2: Solve each system by substitution.A. B.

Example 2: continued...

C. D.

Example 3: Josie is deciding between two cell phone plans. The first plan has a $50 sign-up fee and costs $20 a month. The second plan has a $30 sign-up fee and costs $25 a month.

A. After how many months will the total cost be the same?

B. What will the cost be?

C. If Josie has to sign up for a one year contract, which plan would be cheaper?

If both equations are in standard form:

You must solve one of them for a variable and then

substitute.

Example 4: Solve each system by substitution.

A. B.

Trivia1. Which TV show has the characters:Rachel, Ross, Monica, Joey, Chandler, and Phoebe?

2. Which Disney movie has the characters: Prince Eric, Sebastian, Flounder, Ursula, and King Triton?

Little Mermaid

Friends

Example 4: Solve each system by substitution.

C. D.

Practice:

Practice 6.2 WS

Homework

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