1. Estimating the Area of a Circle Math 8 Stewart COPY SLIDES THAT HAVE A PENCIL

2. Terms to Know Circumference: The circumference of a circle is the distance around the outside of the circle. It could be called the perimeter of the circle. Circumference: The circumference of a circle is the distance around the outside of the circle. It could be called the perimeter of the circle. Diameter: A straight line going through the center of a circle connecting two points on the circumference. Diameter: A straight line going through the center of a circle connecting two points on the circumference.

3. Terms to Know Radius: The distance from the center of a circle to a point on the circle. Radius: The distance from the center of a circle to a point on the circle. Radius = Diameter/2

4. Estimating the Area of a Circle Let’s begin by looking at the radius of a circle: Let’s begin by looking at the radius of a circle: If we measure the radius of the circle, how big would we say it is?

5. Estimating the Area of a Circle Assignment Question 1: Question 1: a) If we shade in one of the squares as shown right, what a) If we shade in one of the squares as shown right, what is the side length of the shaded square? is the side length of the shaded square? b) How is this side length related to the radius of the circle? c) What is the area of the shaded square? (Remember Area=side x side)

6. Question 2: Question 2: a) If I know the area of one a) If I know the area of one shaded square, how can I shaded square, how can I calculate the area of the four calculate the area of the four shaded squares to the right? shaded squares to the right? b) What is the total area of all four squares? b) What is the total area of all four squares? c) Would you say the area of the circle is less than, greater than or equal to the area of the four squares? Explain your choice! c) Would you say the area of the circle is less than, greater than or equal to the area of the four squares? Explain your choice!

7. Question 3: Question 3: a) Do you think an estimate for the area of the circle is closer to 4r 2 or 3r 2. Explain your choice! a) Do you think an estimate for the area of the circle is closer to 4r 2 or 3r 2. Explain your choice! b) Copy and complete the statement below: b) Copy and complete the statement below: The area of a circle is approximately equal to The area of a circle is approximately equal to ___ x the square of the radius. ___ x the square of the radius.

8. Calculating Area of a Circle Using the Radius: Using the Radius: Calculate the area of a circle with a radius of 3cm.

9. Calculating Area of a Circle Using the Diameter: Using the Diameter: Radius = Diameter/2 Calculate the area of a circle with a diameter of 3600m.

10. Practice Find the area of a circle with a radius of 5cm. Find the area of a circle with a radius of 5cm. Find the area of a circle with a diameter of 20m. Find the area of a circle with a diameter of 20m.