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guided note pages for calculating circumference and area of circles

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- 1. Love of Learning Educational Services Bringing Curiosity, Relevance, and Enjoyment to the Math ClassroomCircle NotesCircumference and Area of CirclesGuided note taking pages for calculating circumference and area of circles. 2/13/2011 www.loledservices.com
- 2. Circle NotesParts of a circle: Area center radius diameter Circumference Vocabulary: Vocabulary: diameter – line segment that goes from edge to edge and through the center of a circle radius – line segement that goes from the center to the edge of a circle Circumference – the distance around the outside of the circle Area – the measure of the inside of a circle (always measured in square units) C Pi – the ratio of the Circumference to the diameter of the circle ----- d is the symbol for Pi Pi is approximately 3.14 because it takes a little more than 3 diameters to go around the Circumference of any circle. Special Relationships within a Circle: The diameter is ____________ the radius. The radius is ____________ the diameter. The Circumference is about ____________ the diameter. The diameter is ____________ the Circumference. The Circumference is about ____________ the radius. The radius is about ____________ the Circumference. ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 3. Calculating CircumferenceIf we know the radius or the diameter of a circle, we can find the Circumference. Circumference Formulas C = d or C = 2r 3.14Sample Problems: 1 What is the Circumference of this circle?_________ 5 in Think about it: Which is given, the radius or the diameter? So, which formula should we use? Work it out: Work it out: 1. Write the formula. 2. Plug in the numbers. Step 1: C = d 3. Multiply to get the answer. Step 2: C = 3.14(5) 4. Label the answer with the correct measurement. Step 3: C = 15.7 in This answer makes sense because 3 x 5 = 15. is just a little more than 3, so a little bit more than 15 makes sense. ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 4. What is the Circumference of 2 this circle?_________ 4 in Think about it: Which is given, the radius or the diameter? So, which formula should we use?Work it out: Work it out: 1. Write the formula. 2. Plug in the numbers. Step 1: ____________ 3. Multiply to get the answer. Step 2: ____________ 4. Label the answer with the correct measurement. Step 3: ____________ This answer makes sense because: What is the Circumference of 3 this circle?_________ 6 cm Think about it: Work it out:Which is given, the radius or the diameter? Step 1: ____________So, which formula should we use? Step 2: ____________ Step 3: ____________ This answer makes sense because: ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 5. What is the Circumference of 4 this circle?_________ 2m Think about it: Which is given, the radius or the diameter? Work it out: Step 1: ____________ So, which formula should we use? Step 2: ____________ Step 3: ____________ This answer makes sense because: What is the Circumference of 5 this circle?_________ 9 cm Think about it: Which is given, the radius or the diameter? Work it out: Step 1: ____________ So, which formula should we use? Step 2: ____________ Step 3: ____________ This answer makes sense because: Work it out: Work it out:6 7 Step 1: ____________ Step 1: ____________ Step 2: ____________ Step 2: ____________8 cm Step 3: ____________ 5 in Step 3: ____________ ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 6. Calculating Area of a CircleIf we know the radius or the diameter of a circle, we can find the Area. We always have to square the radius before we multiply by . Area Formula r 2 means r r so A r 2 A r 2 means A (r r ) 3.14Sample Problems: 1 What is the Area of this circle?_________ 6 in Think about it: Which is given, the radius or the diameter? d ÷ 2 = r So, what is the radius? Work it out: Work it out: 1. Write the formula. 2. Plug in the numbers. Step 1: A = r 2 Step 2: A = 3.14(32) 3. Square the radius. (Multiply radius x radius) 4. Multiply to get the answer. Step 3: A = 3.14(9) 5. Label the answer with the correct measurement. Step 4: C = 28.26 in2 This answer makes sense because 3 x 9 = 27. is just a little more than 3, so a little bit more than 27 makes sense. ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 7. What is the Area of this 2 circle?_________ 4 in Think about it: Which is given, the radius or the diameter? So, what is the radius? Work it out: Work it out: 1. Write the formula. Step 1: ____________ 2. Plug in the numbers. Step 2: ____________ 3. Square the radius. (Multiply radius x radius) 4. Multiply to get the answer. Step 3: ____________ 5. Label the answer with the correct measurement. Step 4: ____________ This answer makes sense because: What is the Area of this 3 circle?_________ 6 cm Think about it: Work it out: Step 1: ____________Which is given, the radius or the diameter? Step 2: ____________So, what is the radius? Step 3: ____________ Step 4: ____________This answer makes sense because: ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 8. What is the Area of this 4 circle?_________ 2m Think about it: Work it out: Which is given, the radius or the diameter? Step 1: ____________ Step 2: ____________ So, what is the radius? Step 3: ____________ Step 4: ____________ This answer makes sense because: What is the Area of this 5 circle?_________ 9 cm Think about it: Work it out: Which is given, the radius or the diameter? Step 1: ____________ So, what is the radius? Step 2: ____________ Step 3: ____________ This answer makes sense because: Step 4: ____________ Work it out: Work it out: 6 7 Step 1: ____________ Step 1: ____________Find Area: Find Area: Step 2: ____________ Step 2: ____________ Step 3: ____________ Step 3: ____________ 4 cm Step 4: ____________ 5 in Step 4: ____________ ©2011 Love of Learning Educational Services, LLC. All rights reserved.
- 9. 8 Mrs. Davis wants to paint the top of a circular table that has a diameter of 3 feet. How many square feet will be painted? Think about it: Draw a picture: 3 ft What key words indicate that this is an area problem? Work it out: Which is given, the radius or the diameter? Step 1: ____________ So, what is the radius? Step 2: ____________ Step 3: ____________ Step 4: ____________ This answer makes sense because: Mr. Magoo wants to put a circular rug in his office. His 8 foot long rectangular 9 desk will sit directly across the center of the rug from one side to the other. How big is the rug that Mr. Magoo wants to purchase? Think about it: Draw a picture: What key words indicate that this is an area problem? Work it out: Which is given, the radius or the diameter? Step 1: ____________ So, what is the radius? Step 2: ____________ Step 3: ____________This answer makes sense because: Step 4: ____________ ©2011 Love of Learning Educational Services, LLC. All rights reserved.

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