# Exponential functions

Our textbook defines an exponential function as
f(x) = ab^x. However, a question was brought up about a function, g(x) = 5^sqrt(x). Is g an exponential function? It looks like an exponential graph for x>0, but is not continuous on R.

## Answers and Replies

dextercioby
Homework Helper
A function is not defined in the absence of domain and range. So do tell us the whole definition as worded by your book.

jbriggs444
Homework Helper
2019 Award
Our textbook defines an exponential function as
f(x) = ab^x. However, a question was brought up about a function, g(x) = 5^sqrt(x). Is g an exponential function? It looks like an exponential graph for x>0, but is not continuous on R.
Let us ignore the fact that g(x) = 5^sqrt(x) is not always real-valued for negative x and ask the somewhat better defined question:

"Does the graph of g(x) = 5^sqrt(x) match the graph of any function f(x) of the form ab^x for real-valued constants a and b and positive real x"

One simple-minded way to answer this would be to assume that there is such a function and realize that, if so:

f(0) = a*b^0 = a = g(0) = 5^sqrt(0) = 1

So a = 1

f(1) = a*b^1 = ab = b = g(1) = 5^sqrt(1) = 5

So b = 5

So the question then becomes:

"does the graph of g(x) = 5^sqrt(x) match the graph of f(x) = 5^x"

The answer to that question is rather obvious.