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U1l1t Solving by Graphing

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L1 – Solving Linear Systems by GRAPHING Unit 1

MPM2D
Jensen

Linear System: Two or more linear equations that are considered at the same time.

Point of Intersection: The point where 2 or more lines cross.

To solve a linear system means to find the values of the variables that satisfy ALL of the equations in the
system. Graphically speaking, this means you will find the ordered pair (𝑥, 𝑦) where the lines intersect.

There are 3 main methods for solving a linear When solving by graphing, you can graph the lines
system: by:

1) Graphing 1) Using the slope and 𝑦-intercept (rearrange in to


2) Substitution 𝑦 = 𝑚𝑥 + 𝑏 form)
3) Elimination 2) Use the 𝑥 and 𝑦 intercepts of each line
3) Create a table of values for each equation

A linear system could have 1, 0, or infinitely many solutions:

Graph Slopes of Lines Intercepts Number of Solutions


Intersecting

Usually different
DIFFERENT unless the lines 1
intersect on an axis

Parallel & Distinct

Same Different 0

Parallel & Coincident

Same Same Infinitely Many


Steps for Solving a Linear System by GRAPHING

1) Rearrange the equations in to slope 𝑦-intercept form (𝑦 = 𝑚𝑥 + 𝑏)

2) Graph equations and find the point of intersection

3) Verify that the point of intersection satisfies the equation of both lines

4) Clearly communicate your solution

Example 1: Find the point of intersection of the graphs of the following systems of equations.

a) ℓ1 : 𝑦 = 𝑥 + 4
ℓ2 : 𝑦 = −𝑥 + 2

b) ℓ1 : 2𝑥 + 𝑦 = 5
ℓ2 : 𝑥 − 2𝑦 = 10
c) ℓ1 : 2𝑥 + 5𝑦 = −20
ℓ2 : 5𝑥 − 3𝑦 = −15

Note: Our solution to this


system is an estimate. The
solution will not exactly
verify the original equations
but should be close!

d) ℓ1 : 𝑦 = 2𝑥 + 3
ℓ2 : 𝑦 = 2𝑥 − 4

Notice the functions


have the same slope but
different y-intercepts.
They will be parallel but
distinct.

e) ℓ1 : 𝑥 + 𝑦 = 3
ℓ2 : 2𝑥 + 2𝑦 = 6

Notice the lines have the


same slope and same y-int.
They will be parallel and
coincident

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