Final answer:
The critical value x = 3 obtained from a completely continuous function f' suggests a change in slope from negative to positive at that point.
Step-by-step explanation:
The critical value x = 3 obtained from a completely continuous function f' indicates a critical point where the derivative of the function changes sign. In this case, f'(0) = -1 and f'(5) = 10. This means that the function has a negative slope at x = 0 and a positive slope at x = 5. The critical value of x = 3 falls between these two points, suggesting a change in slope from negative to positive.