6 1 Solving Systems by Graphing Warm Up

6 -1 Solving Systems by Graphing Warm Up Evaluate each expression for x = 1 and y =– 3. 1. x – 4 y 2. – 2 x + y – 5 13 Write each expression in slopeintercept form. 3. y – x = 1 y=x+1 4. 2 x + 3 y = 6 y= 5. 0 = 5 y + 5 x y = –x Holt Algebra 1 x+2

6 -1 Solving Systems by Graphing Objectives Identify solutions of linear equations in two variables. Solve systems of linear equations in two variables by graphing. Holt Algebra 1

6 -1 Solving Systems by Graphing Vocabulary systems of linear equations solution of a system of linear equations Holt Algebra 1

6 -1 Solving Systems by Graphing A system of linear equations is a set of two or more linear equations containing two or more variables. A solution of a system of linear equations with two variables is an ordered pair that satisfies each equation in the system. So, if an ordered pair is a solution, it will make both equations true. Holt Algebra 1

6 -1 Solving Systems by Graphing Example 1 A: Identifying Systems of Solutions Tell whether the ordered pair is a solution of the given system. (5, 2); 3 x – y = 13 0 3 x – y 13 3(5) – 2 13 Substitute 5 for x and 2 for y in each equation in the system. 2– 2 0 15 – 2 13 0 0 13 13 The ordered pair (5, 2) makes both equations true. (5, 2) is the solution of the system. Holt Algebra 1

6 -1 Solving Systems by Graphing Helpful Hint If an ordered pair does not satisfy the first equation in the system, there is no reason to check the other equations. Holt Algebra 1

6 -1 Solving Systems by Graphing Example 1 B: Identifying Systems of Solutions Tell whether the ordered pair is a solution of the given system. x + 3 y = 4 (– 2, 2); –x + y = 2 x + 3 y = 4 –x + y = 2 –(– 2) + 2 – 2 + 3(2) 4 – 2 + 6 4 4 2 2 Substitute – 2 for x and 2 for y in each equation in the system. The ordered pair (– 2, 2) makes one equation true but not the other. (– 2, 2) is not a solution of the system. Holt Algebra 1

6 -1 Solving Systems by Graphing Check It Out! Example 1 a Tell whether the ordered pair is a solution of the given system. (1, 3); 2 x + y = 5 – 2 x + y = 1 2 x + y = 5 2(1) + 3 5 2+3 5 5 5 – 2 x + y = 1 – 2(1) + 3 1 – 2 + 3 1 1 1 Substitute 1 for x and 3 for y in each equation in the system. The ordered pair (1, 3) makes both equations true. (1, 3) is the solution of the system. Holt Algebra 1

6 -1 Solving Systems by Graphing Check It Out! Example 1 b Tell whether the ordered pair is a solution of the given system. (2, – 1); x – 2 y = 4 3 x + y = 6 Substitute 2 for x and 3 x + y = 6 – 1 for y in each 3(2) + (– 1) 6 2 – 2(– 1) 4 equation in the 6– 1 6 2+2 4 system. 5 6 4 4 The ordered pair (2, – 1) makes one equation true, but not the other. (2, – 1) is not a solution of the system. x – 2 y = 4 Holt Algebra 1

6 -1 Solving Systems by Graphing All solutions of a linear equation are on its graph. To find a solution of a system of linear equations, you need a point that each line has in common. In other words, you need their point of intersection. y = 2 x – 1 y = –x + 5 The point (2, 3) is where the two lines intersect and is a solution of both equations, so (2, 3) is the solution of the systems. Holt Algebra 1

6 -1 Solving Systems by Graphing Helpful Hint Sometimes it is difficult to tell exactly where the lines cross when you solve by graphing. It is good to confirm your answer by substituting it into both equations. Holt Algebra 1

6 -1 Solving Systems by Graphing Example 2 A: Solving a System Equations by Graphing Solve the system by graphing. Check your answer. y=x Graph the system. y = – 2 x – 3 The solution appears to be at (– 1, – 1). y=x Check Substitute (– 1, – 1) into the system. y = – 2 x – 3 y=x • (– 1, – 1) y = – 2 x – 3 (– 1) – 1 (– 1) – 2(– 1) – 3 – 1 2– 3 – 1 (– 1, – 1) is the solution of the system. Holt Algebra 1

6 -1 Solving Systems by Graphing Example 2 B: Solving a System Equations by Graphing Solve the system by graphing. Check your answer. y=x– 6 y+ x = – 1 Rewrite the second equation in slope-intercept form. y+ − x = – 1 x y= Holt Algebra 1 − x Graph using a calculator and then use the intercept command. y=x– 6

6 -1 Solving Systems by Graphing Example 2 B Continued Solve the system by graphing. Check your answer. Check Substitute into the system. y=x– 6 + – 1 – 1 Holt Algebra 1 – 1 The solution is .

6 -1 Solving Systems by Graphing Check It Out! Example 2 a Solve the system by graphing. Check your answer. y = – 2 x – 1 y=x+5 Graph the system. The solution appears to be (– 2, 3). y=x+5 y = – 2 x – 1 Check Substitute (– 2, 3) into the system. y = – 2 x – 1 y=x+5 3 3 – 2(– 2) – 1 4 – 1 3 3 (– 2, 3) is the solution of the system. Holt Algebra 1 3 – 2 + 5 3 3

6 -1 Solving Systems by Graphing Check It Out! Example 2 b Solve the system by graphing. Check your answer. 2 x + y = 4 Rewrite the second equation in slope-intercept form. 2 x + y = 4 – 2 x y = – 2 x + 4 Holt Algebra 1 Graph using a calculator and then use the intercept command. 2 x + y = 4

6 -1 Solving Systems by Graphing Check It Out! Example 2 b Continued Solve the system by graphing. Check your answer. 2 x + y = 4 Check Substitute (3, – 2) into the system. – 2 – 2 (3) – 3 1– 3 – 2 Holt Algebra 1 2 x + y = 4 2(3) + (– 2) 4 6– 2 4 4 4 The solution is (3, – 2).

6 -1 Solving Systems by Graphing Lesson Quiz: Part I Tell whether the ordered pair is a solution of the given system. 1. (– 3, 1); no 2. (2, – 4); yes Holt Algebra 1

6 -1 Solving Systems by Graphing Lesson Quiz: Part II Solve the system by graphing. 3. y + 2 x = 9 y = 4 x – 3 Holt Algebra 1 (2, 5)