How do you find the area of a circle knowing only its circumference?

Answer 1

If you know a circle's area, you can easily determine its radius using equation (1). Once you determine r, then plug it into equation (2). Pi = 3.14. (1) A = [Pi]r2 (2) C = 2[Pi]r Hint: Equation (1) can be rewritten r = SQRT(A/Pi)

Answer 2

You need to know a few formulas relating to circles.

Specifically, you need to know that

-- the circumference is (pi) times (the diameter)

-- the radius is (1/2 of the diameter)

-- the area is (pi) times (the radius)2

1). You know the circumference. Use (circumference = pi times diameter) to find the diameter.

2). Then use (radius = 1/2 of diameter) to find the radius.

3). Then use (area = pi times radius2) to find the area.

When you get really good at your algebra, you'll be able to scribble and doodle

with all three of these formulas some rainy afternoon, and MASH them all into

one formula:

(Area)circle = (Circumference)2 divided by (4 pi) .

And later, when you go on to work with spheres, you'll notice the weird and

wonderful similarity when you discover that the surface area of a sphere is

(Area)sphere = (Circumference)2 divided by (pi) .