唔識做ar!

It should bend it in circle.
Circle is the maximum area that can be bend.
First, bend it into a circle and the 40cm wire will be the circumference of the circle.
The formula of the getting the circumference of the circle is :
2πr = 40
We may change the formula in order to get the radius of the circle.
πr = 20
r = 20 / π
The formula of the area of the circle : πr2
The area of the circle above :
πr2 = π(20 / π)2
= 127.32 cm2 , cor to 5 sig. fig.

2009-07-12 15:32:09 補充：
2πr = 40

2009-07-12 15:32:19 補充：
π = pi