(1) arclength ... , where is in radians

how many radians in a quarter circle?

(2) I believe the formula , is fora circle inscribed in a polygonof x sides.

A(6) = 3.464...

A(10) = 3.249...

A(100) = 3.1426...

A(1000) = 3.1416...

A(10000) = 3.14159...

so ... what value is this approaching?

(3) yes, 30 ft = distance from crest to trough ...double the amplitude.