How many ________does it take...

[Obi2Kenobi]

It is one.  The number on top is the derivative of x squared, the number on the bottom is 2x.  the parentheses set off the derivative, so you're not taking to derivative of the whole thing, just the x^2.
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I'm not seeing how you get one. Just substitute any number in for d and x (aside from 0). If d=4 and x=3, for example, then you get

(4/4*3*(3^2))/2*3
(1*3*(9))/2*3
27/2*3
81/2
40.5=(3^4)/2