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Exponential functions

by drewfstr314
Tags: exponential, functions
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drewfstr314
#1
Nov29-12, 09:40 AM
P: 19
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.

Thanks in advance!
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dextercioby
#2
Nov29-12, 12:06 PM
Sci Advisor
HW Helper
P: 11,896
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
#3
Nov29-12, 01:01 PM
P: 907
Quote Quote by drewfstr314 View Post
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.


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