standard_description: Interpret the equation y = mx + b as defining a linear function, whose graph is a straight line; give examples of functions that are not linear. For example, the function A = s2 giving the area of a square as a function of its side length is not linear because its graph contains the points (1,1), (2,4) and (3,9), which are not on a straight line.
problem_activity: Task
Complete the table. In the third column, show your work as demonstrated. What do you notice about the 3rd column?
| $x$ | $y=2x+5$ | $\Delta y$ |
|-----|----------|------------|
|  1  |    7     |    ----    |
|  2  |    9     | 9 - 7 = 2  |
|  3  |          |            |
|  4  |          |            |
|  5  |          |            |
Complete the table, showing your work as above. What do you notice about the 3rd column? What is the graphical interpretation of this?
| $x$ |    $y=ax+b$    |            $\Delta y$             |
|-----|----------------|-----------------------------------|
|  1  | $a\cdot 1 +b$  |                ---                |
|  2  | $a \cdot 2 +b$ | $a\cdot 2+b - (a\cdot 1 + b) = a$ |
|  3  |                |                                   |
|  4  |                |                                   |
|  5  |                |                                   |
Let $y=ax+b$. Let $x_0$ be any particular $x$-value. Show that if $x_0$ is increased by 1, the corresponding $\Delta y$ is a constant that does not depend on $x_0$. What is this constant?
Does (a) serve as an example of the result in (c) ? Explain.


aligns: no