Big Ideas Math: Modeling Real Life, Grade 8
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2. Representations of Functions
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Exercise 13 Page 284

Make a function table to obtain ordered pairs.

Practice makes perfect

To graph the function y=- 2x, we will follow two steps.

  1. Make a function table to obtain ordered pairs.
  2. Graph the ordered pairs and draw the line through them.
Let's do these things one at a time.

Making a Function Table

To make a function table, we will select some values of x which will be part of our domain. Then, we will substitute these values for x to find the corresponding values of y. These x- and y-values will create a set of ordered pairs.

x -2x y (x,y)
0 - 2( 0) 0 ( 0, 0)
- 1 - 2( - 1) 2 ( - 1, 2)
- 2 - 2( - 2) 4 ( - 2, 4)
- 3 - 2( - 3) 6 ( - 3, 6)

We found four ordered pairs that lie on the graph of our function.

Graphing the Ordered Pairs and Drawing the Line

Next, we will graph the ordered pairs and connect them with a straight line.

points and line

The line is the complete graph of the function. The ordered pairs corresponding to any points on the line are solutions of the equation y=- 2x.