Chapter 2: Problem 10
Express the area, \(A\), of a circle as a function of its circumference, \(C\).
Short Answer
Expert verified
The area is \( A = \frac{C^2}{4\pi} \).
Step by step solution
01
Understanding the Relationship
A circle's circumference is given by the formula \( C = 2\pi r \), where \( r \) is the radius. The area is given by \( A = \pi r^2 \). Our goal is to express \( A \) in terms of \( C \).
02
Solve for Radius
From the circumference formula, \( C = 2\pi r \), solve for the radius \( r \). This gives us \( r = \frac{C}{2\pi} \).
03
Substitute Radius into Area Formula
Substitute \( r = \frac{C}{2\pi} \) into the area formula \( A = \pi r^2 \). This becomes \( A = \pi \left( \frac{C}{2\pi} \right)^2 \).
04
Simplify the Area Expression
Simplify \( A = \pi \left( \frac{C}{2\pi} \right)^2 \) by calculating \( \left( \frac{C}{2\pi} \right)^2 \): \[ \left( \frac{C}{2\pi} \right)^2 = \frac{C^2}{4\pi^2} \]Substitute back into the formula: \[ A = \pi \cdot \frac{C^2}{4\pi^2} \]Further simplify to get:\[ A = \frac{C^2}{4\pi} \]
05
Final Expression
The area \( A \) of a circle as a function of its circumference \( C \) is \( A = \frac{C^2}{4\pi} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circumference
The circumference of a circle is like the perimeter we find in polygons. It measures the distance around the circle. To calculate the circumference ( C ), you use the formula: C = 2\pi r . Here, \( r \) represents the circle's radius, and \( \pi \) (pi) is a special mathematical constant approximately equal to 3.14159.
- Role of Pi: Pi helps us understand the relationship between a circle's diameter and its circumference.
- Why Twice the Radius?: Since the radius is half the diameter, multiplying the diameter by \( \pi \) accounts for half the size twice.
- Applications: This formula is useful in finding how long the boundary of a circle is, such as the length of a circular track.
Area of a Circle
The area of a circle tells us how much space is enclosed within its boundary. We calculate it using the formula: A = \pi r^2 , where \( r \) is the circle's radius.
- Pi Again: Just like with the circumference, \( \pi \) is crucial here and relates the square of the radius to the area.
- The Exponent: Squaring the radius ( r^2 ) shows how area grows with the radius; a little change in the radius makes a big change in the area.
- Visualization: Imagine trying to lay small tiles to fill the circle. This tile count is the area.
Radius
The radius of a circle is the distance from its center to any point along its edge. It's a crucial measure in circle geometry. If you think of a circle as a wheel, the radius is like the spoke reaching from the center to the rim.
- Connecting Concepts: The radius links the circle's circumference and area. For instance, both principal formulas for circumference and area use the radius.
- Expressing the Radius: From the circumference formula, \( C = 2\pi r \), you can determine the radius as \( r = \frac{C}{2\pi} \).
- Everyday Geometry: Knowing the radius helps solve practical problems, like finding the right size of a circular carpet or a pizza of a specific size.