Final answer:
To express that a function f is continuous at the number 3, use the limit notation.
Step-by-step explanation:
To express that a function f is continuous at the number 3, we can use the limit notation. We say that f(x) is continuous at x = 3 if lim (x->3) f(x) = f(3). In other words, the limit of f(x) as x approaches 3 should be equal to the value of f(3).
For example, if f(x) = 2x + 1, to show that it is continuous at x = 3, we need to evaluate lim (x->3) (2x + 1) and check if it is equal to f(3). If the limit evaluates to the same value as f(3), then the function is continuous at x = 3.