12.9 Systems of Equations (Substitution)
12.9 Systems of Equations (Substitution)
Systems of Equations
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22 Video Interactions
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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
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00:00:19
What method should we use to solve this problem?
Elimination
Substitution
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00:00:27
Which variable will we substitute for?
y
x
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00:00:32
What will we substitute for x?
- -2
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00:00:35
We are going to substitute for to find
- x
- y
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00:00:42
Re-write the second equation substituting for x
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00:00:54
What is our next step?
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00:01:05
Which variable do I need to solve for?
x
y
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00:01:15
What do I do next?
Subtract 8 from both sides
Add 6 to both sides
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00:01:43
How do I need to write my solution?
x= and y=
As coordinates
As a fraction
In y=mx+b form
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00:01:46
Write your solution as coordinates:
( , )
- -2
- 7
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00:02:28
What are TWO ways you could solve this problem?
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00:02:52
What is the initial value for company A?
5
30
0
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00:03:01
What is my unit rate (m)?
5
30
0
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00:03:10
What is the initial value for company b?
0
10
5
30
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00:03:17
write your equation for company B
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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
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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
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00:04:29
I can substitute this 5x+3...
for x
for y
nowhere
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00:04:45
Substitute 5x+30 for y
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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
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00:05:43
How many gigs of data will the two companies cost the same?
- 6 gigs
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