The stock price for a certain corporation can be approximated for the years 2011 through 2016 by f(x) = 7.8x-221x + 1586, where x =

The stock price for a certain corporation can be approximated for the years 2011 through 2016 by f(x) = 7.8x²-221x + 1586, where x = 11 corresponds to the year 2011. During what year did a local minimum stock price occur?A local extremum occurs at a critical number of f. Because the derivative exists for every x, the only critical number(s) occur where the derivative is zero. Find the derivative of f(x).