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Solving Systems of Equations by Graphing

Learn how to solve systems of linear equations by graphing using tables, graphs, and models. Identify the solutions using graphs.

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Solving Systems of Equations by Graphing

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  1. Lesson Menu Main Idea and New Vocabulary NGSSS Example 1: One Solution Example 2: Real-World Example Example 3: Real-World Example Example 4: No Solution Example 5: Infinitely Many Solutions Five-Minute Check

  2. Solve systems of equations by graphing. • system of equations Main Idea/Vocabulary

  3. MA.8.A.1.3 Use tables, graphs, and models to represent, analyze, and solve real-world problems related to systems of linear equations. MA.8.A.1.4 Identify the solution to a system of linear equations using graphs. NGSSS

  4. One Solution Solve the system y = 3x – 2 and y = x + 1 by graphing. Graph each equation on the same coordinate plane. Example 1

  5. One Solution The graphs appear to intersect at (1.5, 2.5). Check this estimate by replacing x with 1.5 and y with 2.5. Checky= 3x– 2 y= x+ 1 2.5= 3(1.5)– 2 2.5= (1.5)+ 1 2.5 = 2.5  2.5 = 2.5  Answer: The solution of the system is (1.5, 2.5). Example 1

  6. Solve the system y = – x + 3 and y = –x + 2 by graphing. A. (2, 0) B. (0, 3) C. (–2, 2) D. (–2, 4) Example 1 CYP

  7. One Solution PENS Ms.Baker bought 14 packages of red and green pens for a total of 72 pens. The red pens come in packages of 6 and the green pens come in packages of 4. Write a system of equations that represents the situation. Let x represent packages of red pens and y represent packages of green pens. x + y = 14 The number of packages of pens is 14. 6x + 4y = 72 The number of pens equals 72. Answer: The system of equations is x + y = 14 and 6x + 4y = 72. Example 2

  8. FOOD Abigail and her friends bought some tacos and burritos and spent $23. The tacos cost $2 each and the burritos cost $3 each. They bought a total of 9 items. Write a system of equations that represents the situation. A.2x + 3y = 23x + y = 5 B.x + y = 23x + y = 9 C.2x + 3y = 23x + y = 9 D.2x + 3y = 9x + y = 23 Example 2 CYP

  9. y = –x + 18 One Solution PENS Ms.Baker bought 14 packages of red and green pens for a total of 72 pens. The red pens come in packages of 6 and the green pens come in packages of 4. The system of equations that represents the situation is x + y = 14 and 6x + 4y = 72. Solve the system of equations. Interpret the solution. Write each equation in slope-intercept form. x + y = 14 6x + 4y = 72 y = –x + 14 4y = –6x + 72 Example 3

  10. One Solution Choose values for x that could satisfy the equations. Both equations have the same value when x = 8 and y = 6. You can also graph both equations on the same coordinate plane. Example 3

  11. One Solution Answer: The equations intersect at (8, 6). The solution is (8, 6). This means that Ms. Baker bought 8 packages of red pens and 6 packages of green pens. Example 3

  12. FOOD Abigail and her friends bought some tacos and burritos and spent $23. The tacos cost $2 each and the burritos cost $3 each. They bought a total of 9 items. The system of equations that represents the situation is x + y = 9 and 2x + 3y = 23. Solve the system of equations. Interpret the solution. A.(4, 5); They bought 4 tacos and 5 burritos. B.(4, 5); They bought 4 burritos and 5 tacos. C.(5, 4); They bought 5 tacos and 4 burritos. D.(6, 3); They bought 6 tacos and 3 burritos. Example 3 CYP

  13. No Solution Solve the system y = 2x – 1 and y = 2x by graphing. Graph each equation on the same coordinate plane. Example 4

  14. No Solution The graphs appear to be parallel lines. Since there is no coordinate point that is a solution of both equations, there is no solution for this system of equations. Answer: no solution Example 4

  15. Solve the system y = –x – 4 and x + y = 1by graphing. A. (2.5, –1.5) B. (–2.5, –6.5) C. no solution D. infinitely many solutions Example 4 CYP

  16. Infinitely Many Solutions Solve the system y = 3x − 2 and y − 2x = x − 2 by graphing. Write y − 2x = x − 2 in slope-intercept form. y – 2x = x – 2 Write the equation. y – 2x + 2x = x – 2 + 2x Add 2x to each side. y = 3x – 2 Simplify. Both equations are the same. Graph the equation. Example 5

  17. Infinitely Many Solutions Any ordered pair on the graph will satisfy both equations. So, there are infinitely many solutions of the system. Answer: infinitely many solutions Example 5

  18. Solve the system y = – x + 2 and 3x + 2y = 2 by graphing. A. (0, 2) B. (2, –1) C. no solution D. infinitely many solutions Example 5 CYP

  19. Last year, Justin and his sister, Karin, earned a total of $468 in allowance. If Justin earned $52 more than Karin in allowance, write a system of equations that represents their allowances. A.j + k = 468C.j + k = 468 j = 52 + kj = 52 – k B.j + k = 468 D.j – k = 468 k = 52 + jj = 52 + k Five Minute Check 1

  20. Mrs. Kung spent the same amount on two programs at the local recreation center. The aerobics class costs an initial fee of $10 plus $3 per class. The pottery class costs an initial fee of $6 plus $5 per class. Write a system of equations to represent the cost for the two programs. A.10x + 3x = yC.10 + 3x = y 6x + 5x = y 6 + 5x = y B.10x + 3 = yD.–10 + 3x = y6x + 5 = y –6 + 5x = y Five Minute Check 2

  21. The sum of Dewan’s age and three times Adrianne’s age is 32. The difference between Dewan’s age and Adrianne’s age is 4. Which system can be used to find Dewan’s age and Adrianne’s age? A.d + 3a = 323d − a = 4 B. 3d + a = 32 a − d = 4 C.d + 3a = 32d − a = 4 D.d + 3 + a = 32d − a = 4 Five Minute Check 3

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