Elementary Geometry for College Students (7th Edition)

Published by Cengage
ISBN 10: 978-1-337-61408-5
ISBN 13: 978-1-33761-408-5

Chapter 8 - Section 8.4 - Circumference and Area of a Circle - Exercises - Page 384: 32


A = $\pi r^{2}$ We know d = 2r r = $\frac{d}{2}$ A = $\pi (\frac{d}{2})^{2}$ = $\pi \frac{d^{2}}{4}$

Work Step by Step

Given length of diameter of the circle = d We need to explain why A(circle) = $\frac{\pi}{4} d^{2} $ The area A of a circle whose radius has length r is given by A = $\pi r^{2}$ We know d = 2r r = $\frac{d}{2}$ By putting r = $\frac{d}{2}$ in area formula A = $\pi (\frac{d}{2})^{2}$ = $\pi \frac{d^{2}}{4}$ Therefore A = $\pi \frac{d^{2}}{4}$
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