Circle notes

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guided note pages for calculating circumference and area of circles

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Circle notes

  1. 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. 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. 3. Calculating CircumferenceIf we know the radius or the diameter of a circle, we can find the Circumference. Circumference Formulas C = d or C = 2r   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. 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. 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. 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. 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. 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. 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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