How to figure out the diameter of a circle by its circumference?

The formula I have to go by with the ABYC is normally 3.142xR虏 to know the circle's circumference, but what I am having a hard time with is this, doing it in reverse. Ok, here's where I come into the Land of Confusion (a great Phil Collins/Genesis song btw). Let's say to find the circumference of an 8 inch circle I go with (R)4虏 = 16 * 3.142 = 50.27 inches. But in reverse by dividing 16 by 3.142 I get 5.1 as my radius.





The reason why I need to know this madness, is that I am trying to find out what a non-circular geometrical shape's circular diameter. For example, a triangle with three sides of equal size (3 inches) would give me the circumference reference of the circle, but not its diameter.





I must have slept in my Geometry class back in 1985 and missed this one. Proofs and Theorims were my bane of existence in those horrible days of mullets running amok!





If you can show me the correct formula, you will earn 10 brownie points. :) Everyone loves brownies right?





tyHow to figure out the diameter of a circle by its circumference?
The formula for circumference is C = 蟺d = 2蟺r. What you're remembering is the formula for area, A = 蟺r虏.





If the circumference is 50, solve 50 = 蟺d for diameter by dividing by 蟺, d = 50/蟺 = 15.915.





If the AREA is 50, solve 50 = 蟺r虏 for r by dividing by 蟺 and then taking the square root:





50 = 蟺r虏


50/蟺 = r虏


鈭?50/蟺) = r = 3.99





You can find the circumcenter of a triangle (center of the circle the triangle's 3 corners would sit on) by constructing the perpendicular bisectors of 2 of the sides. The center is the point of intersection. See link.How to figure out the diameter of a circle by its circumference?
How to figure out the diameter of a circle by its circumference?





Circumference = 2 pi r


r = Circumference/2 pi


diameter = 2r


diameter = Circumference/pi
(EDIT: No, you're still not making any sense.)





First of all, you're confusing the formulas for a circle's area and a cirlce's circumference. The AREA of a circle of radius r is


A = 蟺 r^2.





The CIRCUMFERENCE for a circle of radius r is


C = 2 蟺 r





Remember that the diameter is just twice the radius, so you could say C = 蟺 d too. Dividing both sides by 蟺 gives C/蟺 = d. So if you have the circumference of a circle and want to know the diameter, just divide by 蟺 (using an approximation like 3.14, or perhaps the better one you give of 3.142).
There are 2 key formulas for a circle:


Area = 3.14 R^2


Circumference =3.14D. or 3.14(2R)





In your work, 16(3.142)=50.27 is the AREA of the circle, not its circumference


To get the correct circumference, C = 2pi)R


=2(3.142)(4)


=25.136





I hope this helps
Why are you dividing 16 by pi? You should be dividing 50.27 by pi to get back to 16, then take the square root of 16 to get back to 4.
To get to Circum. you need








C=pi(d)





Just plug in the values and just finish the simple equation...
Circumference = diameter x pi; diameter = circumference / pi QED. Your formula is for area, not circumference.
If u r trying to calculate a circunference, maybe the problem is u r using the formula for calculating an area. U should try using 3.14 x diameter


G. luck
It looks like you're using the formula for area, rather than circumference.





A = 3.14r^2


C = 3.14d, or 2(3.14)r





I think that should help.


Just divide the circumference by pi, and you have your diameter.