# 5-4

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## 5-4

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1. 5-4 Solving Special Systems Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 1 Holt Algebra 1

2. Objectives Solve special systems of linear equations in two variables. Classify systems of linear equations and determine the number of solutions.

3. y = x – 4 Show that has no solution. –x + y = 3 y = x – 4 y = 1x –4 –x + y = 3 y = 1x + 3 Example 1: Systems with No Solution Method 1 Compare slopes and y-intercepts. Write both equations in slope-intercept form. The lines are parallel because they have the same slope and different y-intercepts. This system has no solution.

4. y = x – 4 Show that has no solution. –x + y = 3  –4 = 3 Example 1 Continued Method 2 Solve the system algebraically. Use the substitution method because the first equation is solved for y. Substitute x – 4 for y in the second equation, and solve. –x + (x – 4) = 3 False. This system has no solution.

5. y = x – 4 Show that has no solution. –x + y = 3 Example 1 Continued Check Graph the system. –x + y = 3 The lines appear are parallel. y = x– 4

6. y =–2x + 5 Show that has no solution. 2x + y =1 y = –2x + 5 y = –2x + 5 2x + y = 1 y = –2x + 1 Check It Out! Example 1 Method 1 Compare slopes and y-intercepts. Write both equations in slope-intercept form. The lines are parallel because they have the same slope and different y-intercepts. This system has no solution.

7. y =–2x + 5 Show that has no solution. 2x + y =1  5 = 1 Check It Out! Example 1 Continued Method 2 Solve the system algebraically. Use the substitution method because the first equation is solved for y. Substitute –2x + 5 for y in the second equation, and solve. 2x +(–2x + 5) = 1 False. This system has no solution.

8. y =–2x + 5 Show that has no solution. 2x + y =1 Check It Out! Example 1 Continued Check Graph the system. y = –2x + 5 y = – 2x + 1 The lines are parallel.

9. y =3x + 2 Show that has infinitely many solutions. 3x – y +2= 0 y = 3x + 2 y = 3x + 2 3x – y + 2= 0 y = 3x + 2 Example 2A: Systems with Infinitely Many Solutions Method 1 Compare slopes and y-intercepts. Write both equations in slope-intercept form. The lines have the same slope and the same y-intercept. If this system were graphed, the graphs would be the same line. There are infinitely many solutions.

10. y =3x + 2 Show that has infinitely many solutions. 3x – y +2= 0 y = 3x + 2 y − 3x = 2 3x − y + 2= 0 −y + 3x = −2  0 = 0 Example 2A Continued Method 2 Solve the system algebraically. Use the elimination method. Write equations to line up like terms. Add the equations. True. The equation is an identity. There are infinitely many solutions.

11. y = x – 3 Show that has infinitely many solutions. x – y –3 = 0 y = x – 3 y = 1x –3 x – y –3 = 0 y = 1x –3 Check It Out! Example 2 Method 1 Compare slopes and y-intercepts. Write both equations in slope-intercept form. The lines have the same slope and the same y-intercept. If this system were graphed, the graphs would be the same line. There are infinitely many solutions.

12. y = x – 3 Show that has infinitely many solutions. x – y –3 = 0 y = x – 3 y = x –3 x – y –3 = 0 –y = –x + 3  0 = 0 Check It Out! Example 2 Continued Method 2 Solve the system algebraically. Use the elimination method. Write equations to line up like terms. Add the equations. True. The equation is an identity. There are infinitely many solutions.

13. x + y = 5 y = –1x + 5 4 + y = –x y = –1x – 4 Example 3B: Classifying Systems of Linear equations Classify the system. Give the number of solutions. x + y = 5 Solve 4+ y = –x Write both equations in slope-intercept form. The lines have the same slope and different y-intercepts. They are parallel. The system is inconsistent. It has no solutions.

14. y = 4(x + 1) y = 4x + 4 y –3 = x y = 1x + 3 Example 3C: Classifying Systems of Linear equations Classify the system. Give the number of solutions. y = 4(x + 1) Solve y – 3 = x Write both equations in slope-intercept form. The lines have different slopes. They intersect. The system is consistent and independent. It has one solution.

15. x + 2y = –4 y = x –2 –2(y + 2) = x y = x –2 Check It Out! Example 3a Classify the system. Give the number of solutions. x + 2y = –4 Solve –2(y + 2) = x Write both equations in slope-intercept form. The lines have the same slope and the same y-intercepts. They are the same. The system is consistent and dependent. It has infinitely many solutions.

16. y = –2(x – 1) y = –2x + 2 y = –x + 3 y = –1x + 3 Check It Out! Example 3b Classify the system. Give the number of solutions. y = –2(x – 1) Solve y = –x + 3 Write both equations in slope-intercept form. The lines have different slopes. They intersect. The system is consistent and independent. It has one solution.

17. 2x – 3y = 6 y = x –2 y = x y = x Check It Out! Example 3c Classify the system. Give the number of solutions. 2x – 3y = 6 Solve y = x Write both equations in slope-intercept form. The lines have the same slope and different y-intercepts. They are parallel. The system is inconsistent. It has no solutions.