What is the Fundamental Period of a Function with a Given Derivative?

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Homework Help Overview

The discussion revolves around determining the fundamental period of a function \( f(x) \) given its derivative \( f'(x) = \frac{0.5 - \sin^2 x}{f(x)} \). Participants are exploring the implications of this relationship and the characteristics of periodic functions.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Some participants attempt to rewrite the derivative in a different form to facilitate integration. Others question the clarity of the problem statement and seek confirmation on the definition of "fundamental period." There are discussions about recognizing relationships between \( f(x) \) and its derivative, as well as the implications of periodicity.

Discussion Status

The discussion is active, with participants providing insights and interpretations of the problem. Some have suggested potential approaches to finding \( f(x) \) and its period, while others are clarifying the problem's requirements. There is no explicit consensus on the solution, but productive lines of reasoning are being explored.

Contextual Notes

Participants note that the problem may lack sufficient information about \( f(x) \) and its periodic nature. There is also mention of multiple interpretations regarding the formulation of the problem statement and the options provided for the period.

Krushnaraj Pandya
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Homework Statement


If the derivative of f(x) w.r.t x is (0.5- sin^2x)/f(x) then fundamental period of f(x) is
2. The attempt at a solution
I wrote 1/2-sin^2x as cos2x/2. since f'(x)=cos2x/2f(x) its integral will be f(x), I would be grateful is someone could provide intuition on how to proceed further
 
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What is "fundamental period"? Can you please provide the problem statement exactly as written down (or at least translated as good as you can), since it does not give information about ##f##.
 
Krushnaraj Pandya said:

Homework Statement


If the derivative of f(x) w.r.t x is (0.5- sin^2x)/f(x) then fundamental period of f(x) is
2. The attempt at a solution
I wrote 1/2-sin^2x as cos2x/2. since f'(x)=cos2x/2f(x) its integral will be f(x), I would be grateful is someone could provide intuition on how to proceed further

So: ##2 f(x) f'(x) = \cos(2x),## and you should recognize that ##2 f(x) f'(x)## is the derivative of some function ##F(x)## that is related to ##f(x)## in some way. That allows you to find ##F(x)## and then, from that, to find ##f(x)##, up to a constant of integration (which will not affect the period, if any).
 
Last edited:
Math_QED said:
What is "fundamental period"? Can you please provide the problem statement exactly as written down (or at least translated as good as you can), since it does not give information about ##f##.

I suspect that the problem should have said "A periodic function ##f(x)## satisfies the equation ##f'(x) = (0.5 - \sin^2 x)/f(x).## What is the period of ##f##?"
 
Math_QED said:
What is "fundamental period"? Can you please provide the problem statement exactly as written down (or at least translated as good as you can), since it does not give information about ##f##.
Ray Vickson said:
I suspect that the problem should have said "A periodic function ##f(x)## satisfies the equation ##f'(x) = (0.5 - \sin^2 x)/f(x).## What is the period of ##f##?"
You're interpreting the question correctly, this is a MCQ type question and I have written the statement unaltered- all the data is mentioned. Fundamental period here means the period of the function (e.g 2pi for sinx) etc.Additionally 4 options are provided (but I should be able to get the answer regardless of whether there are options or not) the options are- 1)pi 2)2pi 3)pi/2 4)3pi/2
 
Ray Vickson said:
So: ##2 f(x) f'(x) = \cos(2x),## and you should recognize that ##2 f(x) f'(x)## is the derivative of some function ##F(x)## that is related to ##f(x)## in some way. That allows you to find ##F(x)## and then, from that, to find ##f(x)##, up to a constant of integration (which will not affect the period, if any).
F(x) will be sin(2x)/2, I am trying to equate ∫2f(x)f'(x) with this now to find f(x)...
 
Krushnaraj Pandya said:
F(x) will be sin(2x)/2, I am trying to equate ∫2f(x)f'(x) with this now to find f(x)...
Got it! I integrated by parts and found f(x)^2=sin2x/2, so the answer is pi. Thanks a lot! :)
 

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