How can you differentiate a function when the variable ( eg x ) is the exponent? Eg F(x)= 2 raised to the x power?

I immerse myself in nuclear physics; where e occurs frequently. I know the derivative of e raised to the x power is the same, but how do you differentiate a function with the variable as the exponent?

Asker: Jeroen, 31 years old

Answer

So the question is, how do you lead the function

f(x) = aX

af, with a being a strict positive number (different from e, and from 1). So an exponential function with base a. The formula for this is f ‘ (x) = aX . ln a

This is very easy to find : since aX always strictly positive you can always take a natural logarithm and then the e-power again. Since the two are each other’s inverse, they cancel each other out. So :

f(x) = exp [  ln ( ax) ]

So by exp I just mean “e to the power”.
Now you know that a logarithm has the following property : ln ab = b . ln a

So : f(x) = exp [ x ln(a) ]

The exponential function aX has thus now been converted into an “ordinary” exponential function.
ln(a) is simply a constant. So now just deduce ;

f'(x) = exp [ x ln(a) ] . ln(a) = exp [  ln(ax) ] . ln(a) = aX . ln(a)

Note that if a is the number e, you indeed “just” have eX finds as a derivative of eX.
After all, ln(e) = 1

Another important consequence : the derivative of af(x)

is thus with the chain rule : af(x) . ln(a) . f’ (x)

How can you differentiate a function when the variable ( eg x ) is the exponent?  Eg F(x)= 2 raised to the x power?

Answered by

prof.dr. Paul Hellings

Department of Mathematics, Fac. IIW, KU Leuven

Catholic University of Leuven
Old Market 13 3000 Leuven
https://www.kuleuven.be/

.

Recent Articles

Related Stories