Well, this is not much of a formula, much more a derivation.
Here goes:
Proof
(A=area, C=Circumference, r=Radius)
∏r2 = A
Multiplying both sides by 2,
2∏r2 = 2A
As 2∏r = C,
Cr = 2A
Cr/2 = A
Here's the trick:
We know that
2∏/2∏ = 1.
So,
Cr/2 x 1 = A.
Cr/2 x 2∏/2∏ = A.
So, we finally have,
Cr x 2∏/2 x 2∏ = A
Again, 2∏r = C,
So,
C x C/4∏ = A
C2/4∏ = A.
For those of you too lazy to read:
Hope this helps!
Go ahead and solve a few problems. They turned out perfect for me!
Oh, and sorry if this thread is too long, but you know math!
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