Final answer:
The equation (k + 1)!= (k + 1) * k! best illustrates the recursive structure of a factorial, where each factorial is calculated based on the previous one multiplied by the new element.
Step-by-step explanation:
The question asks which equation or inequality best exemplifies the recursive nature of a factorial. Out of the given options, choice (d), (k + 1)!= (k + 1) * k!, clearly reflects the recursive structure of a factorial formula. When calculating the factorial of a number, you multiply that number by the factorial of the number immediately preceding it. For example, 4! = 4 * 3!, and this process can be iterated down until you reach the base case, which is 0! = 1, as defined typically in mathematics for the factorial function.