Circumference of a circle

The circumference is the perimeter of a circle - the distance around the outside. It is calculated using the mathematical constant π (pi). **The Formulas:** C = πd (circumference = pi × diameter) C = 2πr (circumference = 2 × pi × radius) **Understanding the Relationship:** - Diameter = 2 × radius - Radius = diameter ÷ 2 - Both formulas give the same answer **The Value of π:** - π ≈ 3.14159... - Use the π button on your calculator for accuracy - Sometimes questions ask for answers in terms of π (e.g., 6π cm) **Choosing Which Formula:** - Use C = πd when given the diameter - Use C = 2πr when given the radius **Rounding Answers:** - Check how many decimal places or significant figures are required - If using π = 3.14, your answer is an approximation **Reverse Problems:** - Given circumference, find diameter: d = C ÷ π - Given circumference, find radius: r = C ÷ 2π **Exam Tips:** - Always check if you have radius or diameter - Leave answers in terms of π if the question asks - State units in your answer (cm, m, etc.) - Use the π button rather than 3.14 for accuracy