Solving By Substitution

Warm-Up!! Please pick up your calculator when you walk in!! Use basic substitution to solve: Y = 3x + 1 when x = 3 2y = x +4 when x = 6 8x + 14 = 2y + 2 when y = 2 Y + 8 = 2x + 10 when y = 4

Substitution Definition Substitution means to replace a variable (letter) with a number that makes the equation or equations true.

Basic Substitution Example: If a = 5, Find the value of y = 4a – 13

Solve by Substitution Not only does substitution mean to replace a variable with a number; you can replace an equation too!

Steps to Solving Systems of Equations by Substitution   Step 1 – Solve an equation for one variable Step 2 – Substitute Step 3 – Solve the equation Step 4 – Plug back in, to other the other variable Step 5 – Check your solution

Example 1) Solve for x and y. x + y = 5 y = 3 + x

Example 2) Solve for x and y. 3x – y = 4 x = 4y – 17

Example 3) 3y + x = 7 4x – 2y = 0

Example 4) y = 2x – 4 y = 4x + 8

You Try! a) 2x + 4y = 4 b) x = 3 – y c) y = 4x 3x + 2y = 22 x + y = 7 3x + y = -21