Unit A Homework

Homework
Name
Geometry & Probability
Date
Unit A
Period
Lesson 4 - Area of Circles
The area A of a circle equals the product of pi (π) and the square of its radius r. A = πr 2
The formula for the area of a semicircle, or half a circle, is A = πr 2 .
Examples
Find the area of the circle.
Use 3.14 for π.
5 cm
Find the area of a semicircle that has a diameter of
9.4 millimeters. Use 3.14 for π. Round to the
nearest tenth.
A = πr 2
Area of semicircle
Area of circle A = πr 2
Replace π with 3.14 and r with 5. A ≈ 3.14 • 5 2
5 2 = 5 · 5 = 25 A ≈ 3.14 • 25
A ≈ 78.5
The area of the circle is approximately 78.5
square centimeters.
A ≈ • 3.14 • 4.7 2 Replace π with 3.14 and
A ≈ 34.7
r with 9.4 ÷ 2 or 4.7.
Multiply.
The area of the semicircle is approximately 34.7
square millimeters.
Exercises
Find the area of each circle. Round to the nearest tenth. Use 3.14 for π. Show your work.
1. _________________ 2. _________________ 3. _________________
7 in
25 mm
12 ft
Find the area of each semicircle. Round to the nearest tenth. Use 3.14 π. Show your work.
4. _________________ 5. _________________ 6. _________________
28 m
3 ft
GARDENING Vidur needs to buy
mulch for the garden with the
dimensions shown in the figure. For
how much area does Vidur need to
buy mulch?
5.5 yd