In the first two topics of this module, you have examined the characteristics and properties of exponential and logarithmic functions. These functions describe many varied phenomena in the world around us, such as:

• Population growth and decline: Human populations tend to grow exponentially, while the populations of endangered animal species decline (or decay) exponentially.
• Making money: When you deposit money in a interest-bearing account, the rate of interest applies to increase the amount exponentially, whether the interest is simple, compounded periodically, or compounded continuously.
• Radioactive material half-life: As we learned in the overview to this module, radioactive materials decay exponentially at different rates known as the material's half-life.

We will examine all of these phenomena, and apply our knowledge of exponential and logarithmic functions to solve problems, in the next topic.