6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/badsubstitution.pdfconclusion the...

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6x + 5y + 11z = 19 2x + 3y + 6z = 6 3x - 2y + 7z = 20

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Page 1: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

Page 2: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

Page 3: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

Page 4: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

Page 5: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

Page 6: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

Page 7: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

− 92 y + 3

2 z = 212

Page 8: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

− 92 y + 3

2 z = 212

− 92

(− 7

4 z − 14

)+ 3

2 z = 212

Page 9: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

− 92 y + 3

2 z = 212

− 92

(− 7

4 z − 14

)+ 3

2 z = 212 z = 1

Page 10: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

− 92 y + 3

2 z = 212

− 92

(− 7

4 z − 14

)+ 3

2 z = 212 z = 1

y = −2

Page 11: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

6x + 5y + 11z = 192x + 3y + 6z = 63x − 2y + 7z = 20

x = 196 − 5

6 y − 116 z

2( 19

6 − 56 y − 11

6 z)+ 3y + 6z = 6

43 y + 7

3 z = − 13

y = − 74 z − 1

4

3( 19

6 − 56 y − 11

6 z)− 2y + 7z = 20

− 92 y + 3

2 z = 212

− 92

(− 7

4 z − 14

)+ 3

2 z = 212 z = 1

y = −2

x = 3

Page 12: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

Conclusion

The substitution method of solving systems of linearequations may work well if there are only 2 variables.If there are 3 or more variables, it can become a nightmare.

Page 13: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

Conclusion

The substitution method of solving systems of linearequations may work well if there are only 2 variables.If there are 3 or more variables, it can become a nightmare.

Page 14: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear
Page 15: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

Page 16: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

Page 17: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

Page 18: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

Page 19: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1

Page 20: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

Page 21: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

Page 22: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

x = 16 (12 − 9y + 5z)

Page 23: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

x = 16 (12 − 9y + 5z) x = −2

Page 24: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

x = 16 (12 − 9y + 5z) x = −2

2x + 3y − 4z ?= 6

Page 25: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

x = 16 (12 − 9y + 5z) x = −2

2x + 3y − 4z ?= 6

2(−2) + 3(1)− 4(−3) = 11

Page 26: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

2x + 3y − 4z = 6−2x + y + 2z = 46x + 9y − 5z = 123x − 2y − 3z = 1

2x + 3y − 4z = 6−2x + y + 2z = 4

4y − 2z = 10

6x + 9y − 5z = 12−6x + 4y + 6z = −2

13y + z = 10

4y − 2z = 1026y + 2z = 2030y = 30

y = 1z = 10 − 13y

z = −3

x = 16 (12 − 9y + 5z) x = −2

2x + 3y − 4z ?= 6

2(−2) + 3(1)− 4(−3) = 11

???

Page 27: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

Conclusion

The addition method of solving systems of linearequations sometimes works well if there are only 2 or 3equations.However, it’s easy to get lost if you don’t keep organized.Far worse, if you just work haphazardly, you can get wronganswers!

Page 28: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

Conclusion

The addition method of solving systems of linearequations sometimes works well if there are only 2 or 3equations.However, it’s easy to get lost if you don’t keep organized.Far worse, if you just work haphazardly, you can get wronganswers!

Page 29: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

Conclusion

The addition method of solving systems of linearequations sometimes works well if there are only 2 or 3equations.However, it’s easy to get lost if you don’t keep organized.Far worse, if you just work haphazardly, you can get wronganswers!

Page 30: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

What We Want

Our DesireWe want a system for solving systems of linear equations that

produces all solutions to the system.never produces fake solutions.is systematic and organized.never requires guesswork to know the next move.

Page 31: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

What We Want

Our DesireWe want a system for solving systems of linear equations that

produces all solutions to the system.never produces fake solutions.is systematic and organized.never requires guesswork to know the next move.

Page 32: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

What We Want

Our DesireWe want a system for solving systems of linear equations that

produces all solutions to the system.never produces fake solutions.is systematic and organized.never requires guesswork to know the next move.

Page 33: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

What We Want

Our DesireWe want a system for solving systems of linear equations that

produces all solutions to the system.never produces fake solutions.is systematic and organized.never requires guesswork to know the next move.

Page 34: 6x 5y 11z 19 x 3y 6z 6 3x 2y 7z 20faculty.cord.edu/ahendric/210/BadSubstitution.pdfConclusion The substitution method of solving systems of linear

What We Want

Our DesireWe want a system for solving systems of linear equations that

produces all solutions to the system.never produces fake solutions.is systematic and organized.never requires guesswork to know the next move.