In this video tutorial, learn to calculate the derivative of the square root of x using the definition of the derivative. As part of this problem, we will go through how to calculate the instantaneous rate of change at a given point in time. Further, we'll examine how to use a position function to find the point in time when an object will be moving at a particular instantaneous rate of change (or velocity) by setting the derivative of the position function to that rate of speed and then solving for the variable.