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# How do you find the circumference of a circle Is it PIE times diameter times 2?

Updated: 10/24/2022

Wiki User

14y ago

Dear confused (not in a rude way, u do seem confused),Circumference=2xPIxR..............is the best way.For example,If the R (radius) is 20m and PI is 3.14 then you times PI 2 times which is 2xPI (3.14)=6.28, THEN YOU times 6.28 by the R (radius)=125.6m rounded to 1 decimal place will leave you with 125.7m and that will be the circumference.With all the best,

Fatima

The above equation |2×Pi×r = circumference| is correct.

The explanation however, is misleading- primarily the two words written IN CAPS. "THEN YOU"

If everything in a formula, or on one side of an equation is being added, subtracted or multiplied, you are free to solve in any order you choose. This rule does NOT apply to division.

The communative property for multiplicationstates that for any numbers a and b, the following is always true:

(a×b) == (b×a)

The associative property for multiplication states that for any numbers a , b, and c , the following is always true:

(a×b)×c == a×(b×c)given that the above are true, the following are also true of our equation...2 × Pi × r 2 × (r × Pi)

using the same example from above, you're given a circle with a radius = 20m.

(2 × 3.14) × 20 == 2 × (3.14 × 20)

plug in Pi(3.14) and r(20) and then choose the order in which you wish to multiply. Think of the commutative property as what it is. The freedom to commute through the steps in any order.

(2 × 3.14) = (6.28)×20 = 125.6m

is the same as... (using the associativeproperty)

(3.14 × 20) = (62.8)×2 = 125.6m

is the same as... (using the commutative property)

(20 × 3.14) = (62.8)×20 = 125.6m

is the same as... oh I dunno... (still using the commutative property)

(2 × 20) = (40)×3.14 = 125.6m

Looking carefully at the order of the last formula, we actually formed a 'new' equation...

(2_×_20)

gave us the diameter(40), which we then multiplied by Pi

(40)×3.14

to get the circumference(125.6m).

= 125.6m

If you have the diameter, don't waste your time with 2*r*Pi. Use the equation

d×Pi = circumference

Wiki User

14y ago