But the V was just the way the Romans wrote the letter U, technically there's no letter V.

More suited, yes, but also it's mandated by European law. That's the actual reason.

There really is an xkcd for everything...

The only theory consistent with the Big Bang is that there is no "before", as the word "before" refers to a point lower than X on the time axis, but time itself was only created with the Big Bang, so the axis came into existence "after" the Big Bang, hence there can't be a "before".

It's like asking "what lies to the North of the North Pole?"

Yeah, same here. Prolonged durations shorter than one hour are bad?

It generally means "how steep is the slope at this point?". The notation dy/dx can be summarized as "how much distance (d) do you go up (y) here for every bit of distance (d) you go sideways (x)?".

So if you have a gentle slope of a lush, rolling hill (or, say, a function y=0.1x+2), then you go up only a little bit when travelling sideways, in this example for every 1 unit of length sideways you only go up by 0.1 of those same units in the upwards direction, so dy/dx is 0.1/1 which is 1/10.

If, on the other hand, you have a sheer cliff of a giant mountain (or, say, y=9x-1), then for every bit you go sideways you go a lot further up, in this example 9 units up per unit sideways, so dy/dx is 9/1 which is 9.

If it's negative, that means you actually go down, not up.

Since you can easily calculate this for every known function f(x), this becomes a handy tool to find out more about that function. For example, if you want to know the maximum points (peaks) of said function, you simply have to find a point where the slope (dy/dx) first goes up (is positive), then goes down (is negative), i.e. it reaches a peak. That means you just find all the places where dy/dx is zero, and then in a second step you probe whether it went from positive to negative (maximum) or vice versa (minimum).