1. Chapter 7 Systems of Equations and Inequalities Copyright © 2014, 2010, 2007 Pearson Education, Inc. 1 7.2 Systems of Linear Equations in Three Variables

2. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 2 Verify the solution of a system of linear equations in three variables. Solve systems of linear equations in three variables. Solve problems using systems in three variables. Objectives:

3. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 3 Systems of Linear Equations in Three Variables and Their Solutions In general, any equation of the form Ax + By + Cz = D where A, B, C, and D are real numbers such that A, B, and C are not all 0, is a linear equation in thre variables, x, y, and z. A solution of a system of linear equations in three variables is an ordered triple of real numbers that satisfies all equations of the system. The solution set of the system is the set of all its solutions.

4. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 4 Example: Determining Whether an Ordered Triple Satisfies a System Show that the ordered triple (–1, –4, 5) is a solution of the system: true

5. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 5 Example: Determining Whether an Ordered Triple Satisfies a System (continued) Show that the ordered triple (–1, –4, 5) is a solution of the system: true The ordered triple (–1, –4, 5) satisfies the three equations. It makes each equation true. Thus, the ordered triple is a solution of the system.

6. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 6 Solving Systems of Linear Equations in Three Variables by Eliminating Variables

7. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 7 Example: Solving a System in Three Variables Solve the system: Step 1 Reduce the system to two equations in two variables.

8. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 8 Example: Solving a System in Three Variables (continued) Solve the system: Step 2 Solve the resulting system of two equations in two variables

9. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 9 Example: Solving a System in Three Variables (continued) Solve the system: Step 3 Use back-substitution in one of the equations in two variables to find the value of the second variable.

10. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 10 Example: Solving a System in Three Variables Solve the system: Step 4 Back-substitute the values found for two variables into one of the original equations to find the value of the third variable. The proposed solution is (1, 4, –3).

11. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 11 Example: Solving a System in Three Variables (continued) Solve the system: Step 5 Check. true

12. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 12 Example: Solving a System in Three Variables (continued) Solve the system: Step 5 (continued) Check. true Substituting (1, 4, –3) into each equation of the system yielded three true statements. The solution set is {(1, 4, –3)}.

13. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 13 Example: Application Find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4). We begin by substituting each ordered pair into the equation To find a, b, and c, we form a system with these equations and solve the system.

14. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 14 Example: Application (continued) Find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4). To find a, b, and c, we will solve the system: Step 1 Reduce the system to two equations in two variables.

15. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 15 Example: Application (continued) To find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4), we are solving the system: Step 1 (cont) Reduce the system to two equations in two variables.

16. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 16 Example: Application (continued) To find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4), we are solving the system: Step 2 Solve the resulting system of equations in two variables.

17. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 17 Example: Application (continued) To find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4), we are solving the system: Step 3 Use back-substitution in one of the equations in two variables to find the value of the second variable.

18. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 18 Example: Application (continued) To find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4), we are solving the system: Step 4 Back-substitute the values found for two variables into one of the original equations to find the value of the third variable.

19. Copyright © 2014, 2010, 2007 Pearson Education, Inc. 19 Example: Application (continued) To find the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4), we have solved the system: We found that a = 3, b = –12, and c = 13. The equation for the quadratic function whose graph passes through the points (1, 4), (2, 1), and (3, 4) is