I always confuse the formula for circumference with the one for area. For a circle of radius 7 cm, which formula do I use and what is the answer?
Circumference is the distance around the circle, and its formula is C = 2 × π × r, where r is the radius. Area uses πr² instead, so the key difference is that circumference has the 2 and a single r, while area squares the radius. Here r = 7 cm and we use π = 22/7. Substitute: C = 2 × (22/7) × 7. The 7 in the radius cancels with the 7 in the denominator: 2 × 22 = 44. So the circumference is 44 cm. The number 7 is chosen in textbooks precisely because it cancels neatly with 22/7. Remember circumference is a length, so the unit is just cm, not square cm.
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