What are some examples of unbounded functions?

1 Answer
Sep 9, 2015

Here are four examples...

Explanation:

x
The simplest example of an unbounded function is f(x) = xf(x)=x, which is unbounded for x in (-oo, oo)x(,)

1/x
The function f(x) = 1/xf(x)=1x is unbounded on any interval that includes x = 0x=0, due to a simple pole at x = 0x=0.

tan(x)
The function f(x) = tan(x)f(x)=tan(x) is unbounded on any interval that includes an xx of the form pi/2 + npiπ2+nπ, since it has a vertical asymptote at each of these values.

Unbounded on any interval

Consider the function:

f(x) = { (0, "if x is irrational"), (q, "if x = p/q in lowest terms and q is odd"), (-q, "if x = p/q in lowest terms and q is even") :}

where p and q are integers and q > 0

This is unbounded on any open interval, since in any open interval you can find a rational number with an arbitrarily large odd or even denominator when expressed in lowest terms.