As a preservatives, Glacial Acetic Acid can be used in a wide variety of industries including: food production, beverage, pharmaceutical, agriculture/animal feed, and various other industries.
The difference quotient is a measure of the average rate of change of the function over an interval (in this case, an interval of length h). The limit of the difference quotient (i.e., the derivative) is thus the instantaneous rate of change.
In the formal definition of the difference quotient, you'll note that the slope we are calculating is for the secant line. A secant line is just any line that passes between two points on a curve. We label these two points as x and (x +h) on our x-axis.