Ignore the other numbers for now; the only important part is our variable x. What's happening is that we take x and cube it, or x * x * x.
this means it is, say, at x = 100, then f(x) = 100 * 100 * 100, or f(x) = 1,000,000.
Now say we put in -100, then f(x) = -100 * -100 * -100, or f(x) = -1,000,000.
Remember, a negative * negative = positive.
Negative * positive = Negative.
So Neg * Neg * Neg --> Pos * Neg --> Neg number
The 1/5 will slow it down, but it won't stop the growth. Taking 4 away is just a joke when we hit numbers that high.