12.9 Systems of Equations (Substitution)

12.9 Systems of Equations (Substitution) 

Systems of Equations 

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22 Video Interactions 


  1. 00:00:16 

    What are the THREE ways to solve a system of equations? 

    • Graphing

       
    • Substitution

       
    • Elimination

       
    • Multiply the equations

       
    • As a friend to solve it for you

       
    • Divide the equations to eliminate a variable

       

  2. 00:00:19 

    What method should we use to solve this problem? 

    • Elimination

       
    • Substitution

       

  3. 00:00:27 

    Which variable will we substitute for? 

    • y

       
    • x

       

  4. 00:00:32 

    What will we substitute for x?   

    • -2 

  5. 00:00:35 

    We are going to substitute for  to find   


  6. 00:00:42 

    Re-write the second equation substituting for x 

     ____________________________ 


  7. 00:00:54 

    What is our next step? 

     ____________________________ 


  8. 00:01:05 

    Which variable do I need to solve for? 

    • x

       
    • y

       

  9. 00:01:15 

    What do I do next? 

    • Subtract 8 from both sides

       
    • Add 6 to both sides

       

  10. 00:01:43 

    How do I need to write my solution? 

    • x=    and y=     

       
    • As coordinates

       
    • As a fraction

       
    • In y=mx+b form

       

  11. 00:01:46 

    Write your solution as coordinates:

    ( , ) 

    • -2 

  12. 00:02:28 

    What are TWO ways you could solve this problem? 

     ____________________________ 


  13. 00:02:52 

    What is the initial value for company A? 

    • 5

       
    • 30

       
    • 0

       

  14. 00:03:01 

    What is my unit rate (m)? 

    • 5

       
    • 30

       
    • 0

       

  15. 00:03:10 

    What is the initial value for company b? 

    • 0

       
    • 10

       
    • 5

       
    • 30

       

  16. 00:03:17 

    write your equation for company B 

     ____________________________ 


  17. 00:03:25 

    What does x represent in the equation? 

    • Number of hours you use your phone

       
    • Number of gigs of data used

       
    • Sign-up fee

       
    • Cell phone company A and cell phone company B

       

  18. 00:03:52 

    If we are trying to find the number of gigs where the two companies are the same, which variable are we solving for? 

    • y

       
    • x

       

  19. 00:04:29 

    I can substitute this 5x+3... 

    • for x

       
    • for y

       
    • nowhere

       

  20. 00:04:45 

    Substitute 5x+30 for y 

     ____________________________ 


  21. 00:05:12 

    What do I need to do now? 

    • Subtract 10x from both sides

       
    • Subtract 30 from both sides

       
    • Subtract 5x from both sides

       
    • Divide both sides by 10

       

  22. 00:05:43 

    How many gigs of data will the two companies cost the same?   

    • 6 gigs 

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