Simple circle problem involving area and circumference

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SUMMARY

The discussion revolves around a mathematical problem involving the area and circumference of a circle formed by ripples in water. The circumference is given as 10 ft, increasing at a rate of 3 ft/s. Participants derive the area as a function of circumference using the formula A = C²/(4π). They explore the relationship between the rate of change of area and circumference, ultimately leading to the conclusion that the rate of change of area can be expressed as dA/dt = (C/2π) * dC/dt.

PREREQUISITES
  • Understanding of basic geometry, specifically the formulas for circumference (C = 2πr) and area (A = πr²) of a circle.
  • Familiarity with limits and the concept of derivatives in calculus.
  • Ability to manipulate algebraic expressions and factor polynomials.
  • Knowledge of the relationship between rates of change in calculus.
NEXT STEPS
  • Study the derivation of the area of a circle in terms of its circumference using algebraic methods.
  • Learn about the application of limits in calculus, particularly in finding derivatives without using traditional differentiation techniques.
  • Explore the concept of related rates in calculus to understand how different quantities change with respect to time.
  • Investigate the implications of the chain rule in calculus for functions defined in terms of other functions.
USEFUL FOR

Students in introductory calculus courses, educators teaching geometry and calculus concepts, and anyone interested in understanding the mathematical relationships between area and circumference in dynamic systems.

  • #31
SteamKing said:
What's the formula for the circumference of a circle?
c=2*##\pi##*r
 
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  • #32
astrololo said:
c=2*##\pi##*r
Sigh... and what happens when you divide C by 2π ?
 
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  • #33
SteamKing said:
Sigh... and what happens when you divide C by 2π ?
You obtian the radius. Btw why are you desesperate lol
 
  • #34
I was hoping you would start working this problem using the method I was leading you to in post #25. This method involves using limits (which is the main requirement for your teacher). If you do what I suggested in post #25 (which is the first step in the derivation), I can lead you through, step by step, to the final result. But I need you to start.

Chet
 
  • #35
$$A(t)=\frac{C^2(t)}{4\pi}$$
$$A(t+Δt)=\frac{C^2(t+Δt)}{4\pi}$$
$$A(t+Δt)-A(t)=\frac{C^2(t+Δt)-C^2(t)}{4\pi}$$
Do you know how to factor the numerator of the right hand side?
 

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