Linear functions are among the simplest and most basic functions you'll learn about, especially in a Grade 9 pre-calculus class. Here are some important features that make them special:

1. Form: Linear functions usually look like this: $y = mx + b$. Here’s what those letters mean:

   • $m$ is the slope, which shows how steep the line is.
   • $b$ is the y-intercept, the spot where the line crosses the y-axis.

2. Graph: When you draw a linear function, you end up with a straight line. This is important because it shows that there is a steady change. There are no curves—just a straight path!

3. Slope: The slope ($m$) tells you how much $y$ changes when $x$ changes. For example, if the slope is 2, then every time you move to the right by 1 (increasing $x$), $y$ goes up by 2. The slope can be positive or negative, which tells you if the line is rising or falling.

4. Domain and Range: Both the domain (all possible $x$ values) and the range (all possible $y$ values) for linear functions go on forever. This means they stretch infinitely in both directions on the graph.

5. Increasing and Decreasing: Depending on the slope, linear functions can either be increasing (positive slope) or decreasing (negative slope). If the slope is zero, the line is flat, showing that $y$ doesn’t change no matter what happens with $x$.

Understanding these features will help you spot linear functions and prepare you for more complicated functions in the future!