Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
Chapter Review
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Exercise 9 Page 227

Start by graphing the given line and then find another line that passes through the point that is the solution to the system.

Example Solution: y=-3x+2 & (I) y=- x+4 & (II)

Practice makes perfect

We want to write a system of linear equations containing the equation y=-3x+2 that has a solution of (-1,5). To do so, let's start by graphing this line in a coordinate plane. We will do this by creating a table of values.

x y=-3x+2 y (x,y)
-1 y=-3( -1)+2 5 ( -1, 5)
0 y=-3( 0)+2 2 ( 0, 2)
1 y=-3( 1)+2 -1 ( 1, -1)

Let's plot the points and connect them with a line.

We want point (-1,5) to be our solution. This means that we need to find another line that passes through (-1,5). To do this, let's choose the slope of the second line to be -1. y= -1x+b ⇒ y=- x+b Now, we will substitute the point ( -1, 5) into the above equation to find the y-intercept b.
y=- x+b
5=-( -1)+b
â–Ľ
Solve for b
5=1+b
4=b
b=4
The value of b is 4. Now we are ready to complete the second equation and write our example system. y=-3x+2 & (I) y=- x+ 4 & (II) Let's add the second line to our graph. We will use a table of values to find points that lie on the line.
x y=- x+4 y (x,y)
-1 y=-( -1)+4 5 ( -1, 5)
0 y=-( 0)+4 4 ( 0, 4)
1 y=-( 1)+4 3 ( 1, 3)

Let's plot the points and connect them with a line.

Notice that this is only an example solution, as we can think of many other systems that satisfy the conditions.