continuity of natural power
Theorem.
Let be arbitrary positive integer. The power function from to (or to ) is continuous at each point .
Proof. Let be any positive number. Denote and . Then identically
Taking the absolute value and using the triangle inequality
give
But since and also , so each summand in the parentheses is at most equal to , and since there are summands, the sum is at most equal to . Thus we get
We may choose ; this implies
The right hand side of this inequality is less than as soon as we still require
This means that the power function is continuous at the point .
Note. Another way to prove the theorem is to use induction on and the rule 2 in limit rules of functions.