03 01 2019 Agenda Bell Ringer Bell ringer

03. 01. 2019 Agenda Bell Ringer • Bell ringer • D. E. A. R. • Circles Video https: //www. youtube. com/ watch? v=O-caw. Byg 2 a. A • Cornell notes: Area of a circle – Topic: Area and circumference of a Circle – E. Q. How do I calculate the Area of a circle? • Summarize Cornell Notes • Two truths, one lie Activity 2*(-9)=18 – Format paper for Cornell notes – D. E. A. R.

Circles • A circle is the set of all points in a plane that are the same distance from a given point, called the center.

Parts of a Circle • Radius-Straight line from the middle to the outside of a circle

• Diameter-a line that cuts the circle in half from end to end

Circumference • Circumference is the distance around the circle. Like the perimeter.

circumference Recap-Circles. The (C) is the distance The diameter (d) is the distance across a circle through the center of the circle. around a circle. The radius (r) is the distance from the center to any point on the circle.

Circles • Pi is a non-terminating and non-repeating number represented by the Greek letter • (pi) • 3. 14 is often used as an approximation for .

Circles • • Formulas for finding Circumference C = d C = 2 r If you are given the diameter in a problem use the formula with d. If you are given a problem with the radius use the formula with r. • Both formulas find the circumference.

Find Circumference • Which formula for C will you use? • C = 2 r • C = 2 (21) • C = 131. 9 inches 21 in

Your Turn Find the Circumference • Which formula for C will you use? • C = d • C = (4. 5) • C = 14. 1 cm 4. 5 cm

Circles - Area • Formula for finding the area of a circle: 2 • A = r • If you are given the diameter instead of the radius; divide the diameter by 2 to get the radius.

Find the Area • D = 14 m r=? • 14 ÷ 2 = 7 m • A = r 14 m 2 • A = (7 2 ) • A = (49) • A = 153. 9 m 2

Your Turn Find the Area • A = r 2 • A = (5 2 ) 5 ft • A = (25) • A = 78. 5 ft 2

Example 3. 14 · 36 = 113. 04 in²

Try

Try

Example 3. 14 · 36 = 113. 04 in²

Try

Try

Radius = 3 Example

Try

Finding Radius and Diameter from Area • Just like you could find radius and diameter from circumference, you can find the radius and diameter from area by filling in known values and solving.

Example Area = �� r² Area = 78. 50 cm² Radius = Diameter =

Area = 314. 00 cm² Radius = Diameter =

Area = 200. 96 cm² Radius = Diameter =

Reference • www. husd. org/cms/lib 08/. . . /Circumference %20 and%20 Area%20 of%20 Circles. ppt • http: //desotoisdmccowanms. ss 10. sharpschool. com/comm on/pages/Display. File. aspx? item. Id=216839 5