Final answer:
The relative minimum or maximum occurs when the derivative is equal to zero because the derivative represents the rate of change of a function.
Step-by-step explanation:
The relative minimum or maximum occurs when the derivative is equal to zero because the derivative represents the rate of change of a function. At a relative minimum or maximum, the rate of change is zero, indicating a point where the function is either increasing or decreasing. By setting the derivative equal to zero and solving for the value of x, we can find the x-coordinate of the relative minimum or maximum.