An exponential function has a standard form of y = a^x + b where x is the degree of the function and b is any constant. An exponential function is used to describe commonly to describe the growth of materials, for example, bacterial growth or even decays, like bacterial decays or radioactive decays. Since there are three variables that are unknown, a, b and x, according to the degrees of freedom rule, we need three points in order to find the function that fits the plotted points. For example, in a bacterial growth problem, we need three separate data that shows population of the bacteria at a specific time.