Limits and Orders of Infinities

Don't be scared!

Infinite means infinite.
Infinitesimal means something is approaching zero.

That's it.

Orders of Infinities

Think about something. Take a few values of and , say, .
You instantly notice that grows much faster than .

If we take infinitely larger values for each, goes up to infinity waaaaaaaaaaaay faster than just .

We say that * is a higher order of infinity than x.

Some elementary functions grow faster than others.

Take for example any form of x with no exponent, 2x, 3x, 100x, 1000x.

A positive power of x larger than 1 will inevitably reach a point where it will grow faster than any of what we just mentioned.

If we put them to a race, our newest competitor, any number raised to the x-th power, so, a constant number c of your choice, in the form will reach a point where it will grow incredibly faster than any power of x. X is now in the exponent.

And finally, the factorial function, which we said is the fastest growing elementary function, as it goes towards infinity, it will take the infinitely many numbers behind it and multiply them all with itself, being the fastest growing function.

But why do we need to know this?

Simple really.

Calculate the following limit:

  • Answer:
    • Simple. If you look in the denominator the will always be larger than any multiple of the other parts of the denominator, so we'll always have a positive value.
    • We have , it grows faster than any of the other monomials in this fraction, so we can literally ignore everything else. This limit is equal to .

Like infinities, numbers getting infinitely larger, we also have our next topic:
The Infinitesimal