Section Summary

In this section, by examining locally linear change in the factors, we have discovered how to find the rate of change of a product. This is summarized in The Product Rule: If `ftext[(]x text[)]=gtext[(]x text[)]htext[(]x text[)]`, then

In variable notation, if `w=ftext[(]x text[)]`, `u=gtext[(]x text[)]`, and `v=htext[(]x text[)]`, then

Each of these formulations tells us that the growth rate of a product is made up of two terms, and each term is one of the factor functions times the growth rate of the other.