Derivative of 4^x: My Exam & Answer Explained

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Discussion Overview

The discussion revolves around finding the derivative of the function 4^x, including various approaches and interpretations of the derivative process. Participants explore the application of logarithmic differentiation and the chain rule in their calculations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents their method of finding the derivative of 4^x, leading to a disagreement with their professor regarding the correctness of their answer.
  • Another participant suggests taking the derivative of ln(y) and substituting y back to arrive at the professor's answer.
  • Several participants discuss the application of the chain rule, with one realizing their initial derivative calculation was incorrect.
  • Another participant confirms that y=e^{xln4} is correct while pointing out ongoing errors in derivative calculations.
  • One participant provides a step-by-step derivation that leads to the instructor's answer, suggesting no need for exponentials in the process.
  • There is a question about why the derivative of ln(4) is not evaluated as 1/4, which is clarified by another participant stating that the derivative of a constant is zero.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of their derivative calculations, with some acknowledging errors while others maintain their approaches. There is no consensus on the initial methods used, but there is agreement on the final derivative form as presented by the instructor.

Contextual Notes

Participants' calculations involve assumptions about the application of differentiation rules, and there are unresolved steps in the reasoning process that lead to different interpretations of the derivative.

whateva
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On my exam, we had to find the derivative of 4^x. This is what I did
Y=4^x
lny=xln4
y=e^xln4
and then finding the derivative for that I got, (xe^(xln4))/4
My professor said that it was wrong and even after I told her what I did to get the answer. She told me the answer was (4^x)ln4 . Which I know it is but I think this is still equivalent to my answer. Was I right? Regardless I still don't get the point :(
 
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take the derivative of \ln(y) and then substitute y back into the result to get the professors answer...
 
whateva said:
y=e^xln4
and then finding the derivative for that I got, (xe^(xln4))/4

How did you get that as the derivative?
 
I did the chain rule, so I got x*1/4*e^xln4 . Which I now realize is wrong, it should've been x*1/4+ln4*e^xln4. But was I right with the y=e^xln4?
 
whateva said:
I did the chain rule, so I got x*1/4*e^xln4 . Which I now realize is wrong, it should've been x*1/4+ln4*e^xln4. But was I right with the y=e^xln4?

You're still doing it wrong but yes ##y=e^{xln4}## is correct
 
$$y = 4^x$$

$$ \ln(y) = \ln(4^x) = x\ln(4)$$

$$\frac{dy}{y} = dx \ln(4)$$

$$\frac{dy}{dx} = y \ln(4) = x^4 \ln(4)$$

proves the instructors answer and no need in taking exponentials...
 
You mean to say that the final answer is:
dy/dx = yln(4) = (4^x)ln(4)
Right?
 
Also, why is derivative of ln(4) not evaluated as 1/4?
 
Because the derivative of a constant is zero.
 
  • #10
Anora said:
You mean to say that the final answer is:
dy/dx = yln(4) = (4^x)ln(4)
Right?

yes, typo...
 

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