Why is the derivative of a circle's area its perimeter?

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SUMMARY

The derivative of a circle's area with respect to its radius is equal to its perimeter, which can be mathematically expressed as da/dr = 2πr. This relationship arises from the area formula A = πr², where the derivative represents the rate of change of area as the radius increases. By considering two circles, one with radius r and another with radius r + dr, the difference in their areas can be approximated geometrically, reinforcing the connection between area and circumference.

PREREQUISITES
  • Understanding of basic calculus concepts, specifically derivatives.
  • Familiarity with the formula for the area of a circle: A = πr².
  • Knowledge of geometric properties of circles, including circumference.
  • Ability to visualize geometric changes and their impact on area.
NEXT STEPS
  • Explore the concept of derivatives in calculus, focusing on geometric interpretations.
  • Study the relationship between area and perimeter in other geometric shapes.
  • Learn about the application of calculus in real-world problems involving circular motion.
  • Investigate the implications of the Fundamental Theorem of Calculus on geometric relationships.
USEFUL FOR

Students studying calculus, mathematics educators, and individuals interested in the geometric interpretation of derivatives.

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Homework Statement



Explain why the relationship of the derivative of a Circle's area is its perimeter makes sense.

Homework Equations



Area of a Cirle=pi*r^2

The Attempt at a Solution


da/dr=2pi*r
2r=diameter and the circumfrece=pi*D so da/dr=Circumfrence
How do i explain why this works?
 
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No idea? Draw a circle of radius r and a circle of radius r+dr. Can't you see a geometric way to approximate the difference in the areas?
 

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