Suppose the circumference of a circle is
4π. What is its area?

Question

Suppose the circumference of a circle is 
4π. What is its area?

igreen · Answer

$\sf C = 2 \pi r$

Find the radius first, then plug it into the formula to find the area.

igreen · Answer

Plug in what we know:

$\sf 4 \pi = 2 \pi r$

Divide 2 pi to both sides

16shuston · Answer

What is the formula for the circumference? When you know this you have to solve for r then take the formula for the area of the circle  and plug in r

anonymous · Answer

$$\frac{ 4 \pi }{ 2 \pi } = \frac{ 2 \pi r }{ 2 \pi } $$

anonymous · Answer

@iGreen  does r=2

igreen · Answer

Yes!

anonymous · Answer

yay!

igreen · Answer

Formula for the area of a circle:

$\sf A = \pi r^2$

Plug in 2 for the radius:

$\sf A = \pi (2^2)$

igreen · Answer

2^2 = ?

anonymous · Answer

$$A=\pi(2^{2})=4 \times3.14= 6.28??$$

igreen · Answer

Yes, but I don't think they want you to simplify pi..

igreen · Answer

If they do, 6.28 is correct..but if they don't, it's $\sf 4 \pi$.

anonymous · Answer

ok i'll let  know in a sec

anonymous · Answer

ya its $$4 \pi$$

anonymous · Answer

Thx so much i get this now i wrote down notes to understand @iGreen

igreen · Answer

Yay! $\Huge\ddot\smile$