 # Area and Circumference of Circles. Circumference of a Circle Formula to MEMORIZE!!!! OR.

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Area and Circumference of Circles

Circumference of a Circle Formula to MEMORIZE!!!! OR

What do the letters stand for? C = circumference r = radius of the circle d = diameter of the circle π = pi. The value of πis “3.14”

Area of a Circle Formula to MEMORIZE!!!!

What do the letters stand for? A = area r = radius of the circle π = pi. The value of πis “3.14”

Question 1 When looking for area, and you only have the diameter, what is the FIRST thing you must do? * Split the diameter in half to get the radius.

Question 2 What is another name for circumference of a circle? * Perimeter!

Example 1 Find the area of a circle with a diameter of 24 in. Answer:

Example 2 Find the circumference of a circle with a diameter of 20 m. Answer:

Example 3 Find the area of a circle with a radius of 6 cm. Answer:

Example 4 Find the circumference of a circle with a radius of 4 km. Answer:

Example 5 The circumference of a circle is 120 mi. What is the diameter to the nearest tenth. Answer:

Example 6 The circumference of a circle is 72 m. What is the radius to the nearest tenth. Answer:

Question What do you notice about the labels between area and circumference? - Area has a squared sign on the unit, but circumference does not.

Question Why do you think the area label has the squared sign? - To find the area, you must ‘square’ the radius.

Challenge What is the area of the square if a circle with a radius of 4 in. is inscribed in a square? 4 in Answer: 64 in 2

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