Final answer:
The critical number of the function y = x⁴/4 is x = 0, found by differentiating and setting the derivative equal to zero.
Step-by-step explanation:
To find the critical numbers of the function y = x⁴/4, we first need to find its derivative because critical numbers occur where the derivative is zero or undefined. The derivative of y with respect to x is y' = x³. Setting y' to zero gives us x³ = 0. Therefore, the only critical number for this function is x = 0.