Some very good answers here.
Change f(x)= 3x^2 + 4x + 2 into "box"
Then plug "box" into the differentiation formula in place of "x".
you get: (box - h) - box / h
now simplify the terms using the real value of "x" (ie. 3x^2 + 4x + 2)
Later on, you will learn "the power rule" which simply states:
where f(x)= x ^ 3
f ' (x)= [exp] x ^ [exp - 1]
ie. f ' (x) = 3x^2
.. much better
In your case:
f(x)=3x^2 + 4x + 2
f ' (x)=6x + 4x + 0
PS: you will notice that the derivitave of any "real number" is always 0