In The Slope of a Line, you learned that the slope, or *m*, of a line describes how rapidly or slowly change is occurring.

Linear Functions have 4 types of slopes: positive, negative, zero, and undefined.

### Negative Slope = Negative Correlation

A negative slope demonstrates a negative correlation between the following:

*x*and*y*- input and output
- independent variable and dependent variable
- cause and effect

**Negative correlation** occurs when the two variables of a function move in opposite directions. Look at the linear function in the picture. As the values of *x* **increase**, the values of *y* **decrease**. Moving from left to right, trace the line with your finger. Notice how the line **decreases**.

Next, moving from right to left, trace the line with your finger. As the values of *x* **decrease**, the values of *y* **increase**. Notice how the line **increases**.

### Real World Examples of Negative Slope

Mr. Nguyen drinks caffeinated coffee two hours before his bed time. The more cups of coffee he drinks (**input**), the fewer hours he sleeps (**output**).

Aisha is purchasing a plane ticket. The fewer days between the purchase date and the departure date (**input**), the more money Aisha will spend on airfare (**output**).

### Calculating Negative Slope

Refer to the PDF, Calculate.Negative.Slope to learn how to use a graph and the slope formula to calculate a negative slope. To download free software to view the PDF, visit http://get.adobe.com/reader/.