Find critical numbers (critical values) of function with square root (radical)

In this example problem, we find the critical numbers or critical values of a function with a square root (radical). By taking the first derivative of the function, we then find one critical number by seeing where the denominator will equal zero. A second is found by setting the first derivative equal to zero and solving for our variable.

[Klyaa]

At 4:07 you say that (1/4)^(2/3) is approximately 0.6299605. This is incorrect! The correct answer to (1/4)^(2/3) is 0.39685. I think you forgot to square your result.