Seftali wrote:

Imagine a tunnel- if the curved portion is 3/4 of a circle and the base of the entrance is 12 ft across- what is the perimeter of the curved portion of the entrance?

The answer is 9pi sqrt 2

can anyone explain?

thanks

U don`t need to post the answer with the question...

Here is my try,

1-draw full circle, then identify 4 points on it, let`s say ABCD, so that distance between each is equal, and it is 1/4 of the circumference.

2-Connect this 4 point, so that square ABCD is formed. note each side of the square is 12.

3- the diameter of the circle is the diagonal of this square, thus equal to

12sqrt(2)

Given the diameter we can calculate circumference, it is 12sqrt(2)p

and since the tunnel is 3/4 of circle circumference, perimeter of the tunnel is 9sqrt(2)pi

it is a good one