Envision Math 2.0: Grade 8, Volume 2
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Envision Math 2.0: Grade 8, Volume 2 View details
2. Solve Systems by Graphing
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Exercise 8 Page 267

Are the equations in slope-intercept form? What information can the slope-intercept form of an equation give us?

Graph:

Solution: Infinitely many solutions.

Practice makes perfect

By graphing the given equations, we can determine the number of solutions to the system. To do this, we will need the equations to be in slope-intercept form to help us identify the slope m and y-intercept b. We will start by transforming the equations a little bit.

Write in Slope-Intercept Form

Let's rewrite each of the equations in the system in slope-intercept form, highlighting the m and b values.

Given Equation Slope-Intercept Form Slope m y-intercept b
2x-3y=6 y= 2/3x+( - 2) 2/3 (0, - 2)
4x-6y=12 y= 2/3x+( - 2) 2/3 (0, - 2)

Graphing the System

To graph our equations, we will start by plotting their y-intercepts. Then, we will use the slope to determine another point that satisfies each equation, and connect the points with a line.

The solutions of the system of equations are the points at which the lines intersect. We can see from our graph that the lines are the same. So, every point on the line is a solution to the system, which means that there are infinitely many solutions.

Showing Our Work

Showing Our Work
In case you want to see the steps we took to rewrite the equations in slope-intercept form, we have included these calculations.

2x-3y=6 & (I) 4x-6y=12 & (II)
- 3y=6-2x & (I) 4x-6y=12 & (II)
- 3y3= 6-2x3 & (I) 4x-6y=12 & (II)
- 3y3= 6-2x3 & (I) -6y=12-4x & (II)
- 3y3= 6-2x3 & (I) -6y6= 12-4x6 & (II)

(I), (II): Write as a difference of fractions

- 3y3= 63- 2x3 & (I) -6y6= 126- 4x6 & (II)

(I), (II): Calculate quotient

- y=2- 2x3 & (I) - y=2- 4x6 & (II)

(I), (II): Commutative Property of Multiplication

- y=2- 23x & (I) - y=2- 46x & (II)

(I), (II): Rearrange equation

- y=- 23x+2 & (I) - y=- 46x+2 & (II)

(I), (II): LHS * (- 1)=RHS* (- 1)

- y* (- 1)=(- 23x+2)* (- 1) & (I) - y* (- 1)=(- 46x+2)* (- 1) & (II)

(I), (II): - a(- b)=a* b

y=(- 23x+2)* (- 1) & (I) y=(- 46x+2)* (- 1) & (II)

(I), (II): Distribute - 1

y= 23x-2 & (I) y= 46x-2 & (II)
y= 23x-2 & (I) y= 23x-2 & (II)

Notice that the obtained equations are identical.