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In order to find the diameter, multiply the radius by 2 d = 2r In order to find the radius, divide the diameter by 2. r = d÷2 cm cm cm cm ft ft in in m m m m To find circumference multiply the diameter by pi (3.14). C = πd Use 3.14 for pi (π) cm If you are given the radius then multiply by 2 to find the diameter then multiply by pi (3.14) C = π(2r) Use 3.14 for pi (π) cm Mixed Practice: Remember: C = πd or C = π(2r) Use 3.14 for pi (π) m Use 3.14 for pi (π) in Use 3.14 for pi (π) in Use 3.14 of pi (π) in In order to find the diameter of a circle, take the circumference and divide by pi (3.14) Diameter = Use 3 for pi (π) 102 in in Diameter = Use 3.1 for pi (π) 136.4 m m In order to find the radius, take the circumference and divide by pi (3.14). Then divide by 2. Radius = Diameter = Use 3 for pi (π) 138 cm cm cm Diameter = Radius = Use 3 for pi (π) 180 m m m Since circumference is found by diameter x π then the number attached to π is the diameter. For example: if C=12π then 12 is the diameter. A circle's circumference is 12π. What is the diameter? The circumference of a circle 22π. What is the diameter? Don't forget: to find the radius you take the diameter and divide by 2 The circumference of a circle is 18π. What is the radius? The circumference of a circle is 32π. What is the radius? The circumference of a circle is 13π. What is the diameter and the radius? Diameter = Radius = |