Opening Activity 1. Find the circumference of a circle with a diameter of 8 ft. Round to the nearest tenth. C= 3.14(8)= 25.1 ft 2. Find the circumference.

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Presentation transcript:

Opening Activity 1. Find the circumference of a circle with a diameter of 8 ft. Round to the nearest tenth. C= 3.14(8)= 25.1 ft 2. Find the circumference of a volcano that has a diameter of 5 miles. Round to the nearest tenth. C=3.14(5)=15.7mi Please clear off your desk except for your homework, opening activity, and pen/pencil!

Chapter 8 Lesson 2 Area of Circles

Objective: Students will find the area of circles.

The area A of a circle equals the product of pi and the square of its radius r. r Example 1: Find the area of a circle with a radius of 3.2 centimeters. Round to the nearest tenth. A=(3.14)(3.2)(3.2) A= A=32.2 square cm (rounded to the nearest tenth)

Example 2: The bottom of a circular swimming pool with a diameter of 30 feet is painted blue. How many square feet are blue? Round to the nearest tenth. Draw a picture30 ft For our area equation, we need radius, which is one half of the diameter, so to find radius we must divide the diameter by 2. r=15 ft A=(3.14)(15)(15) A=706.5 square feet

A semicircle is half a circle. The formula for the area of a semicircle is: Example 3: Find the approximate area of a semicircle with a radius of 6 centimeters. Round to the nearest tenth. A=56.52 Round to the nearest tenth

Example 4: Tarie is cutting material in the shape of semicircles with a diameter of 16 in for her craft project. What is the are of the semicircle? Round to the nearest tenth if necessary. A=100.48