1. MJ2 Ch 11.6 – Area of Circles

2. Bellwork  Find the area of the triangle to the nearest tenth. Use the formula A = ½bh 26.1 cm 29.3 cm 30.5 cm

3. Bellwork Solution A = ½bh 26.1 cm 29.3 cm 30.5 cm A = ½(764.73) A = ½(26.1)(29.3) A = 382.365 A = 382.4 cm 2 1. Write the formula 2. Substitute 3. Do the math

4. Assignment Review  Text p. 491 # 8 – 15  Note: Your bellwork is due today…Please pass it forward…

5. Before we begin  Please take out your notebook and get ready to work…  Continuing with the theme of area, in today’s lesson we will look at how to calculate the area of a circle  Of course, you will use a formula and the formula method to demonstrate what you know….

6. Objective  Students will calculate the area of circles

7. Vocabulary  In a previous lesson we defined the parts of a circle…so this should be a quick review  Diameter – the distance across a circle through the center  Radius – the distance from the center to any point on the circle  Pi (3.14) – the numerical expression that represents the relationship between the diameter and circumference of a circle

8. Circles  To calculate the area of a circle use the formula A = ∏r 2  Be careful here….the formula calls for r.  If you are given d, you have to convert it to r  We all remember that r is ½ of d

9. Example #1 A = ∏r 2 6.5 m A = (3.14)(6.5) 2 A = 3.14(42.25) A = 132.665 A = 132.7 m 2 1. Write the formula 2. Substitute 3. Do the math Your answer will be squared because you are measuring 2 dimensions

10. Example #2 A = ∏r 2 16 m A = (3.14)(8) 2 A = 3.14(64) A = 200.96 A = 200.96 m 2 1. Write the formula 2. Substitute 3. Do the math Since you are given the diameter you have to convert it to radius to use in the formula

11. Your Turn  In the notes section of your notebook draw and label the circle and then calculate area to the nearest tenth using the formula A = ∏r 2 6 yd 4 cm 1.2.

12. Your Turn Solution #1 A = ∏r 2 4 cm A = 3.14(4) 2 A = 3.14(16) A = 50.24 A = 50.2 cm 2 1. Write the formula 2. Substitute 3. Do the math

13. Your Turn Solution #2 A = ∏r 2 A = 3.14(3) 2 A = 3.14(9) A = 28.26 A = 28.3 yd 2 1. Write the formula 2. Substitute 3. Do the math 6 yd

14. Summary  In the notes section of your notebook summarize the key concepts covered in today’s lesson  Today we discussed: Calculating area of circles What method do you use? What do you do if they give you the diameter?

15. Assignment  Text p. 494 # 11 – 20 Reminder This assignment is due tomorrow I do not accept late assignments Draw and label the picture and use the formula method Answers only will not be accepted for a grade