Hello Frans and list-watchers, There's an easier route than integrals; but I can't do the no maths solution yet.
Ramanujan came up with an approximation:
( 3(a + b) - sqrt[ (a + 3b)(3a + b) ] ) pi
for major and minor half axes a and b.
For example, if a = b, this approximation reduces to
( 3(a + a) - sqrt[ (a + 3a)(3a + a) ] ) pi
( 6a - sqrt[ (4a)^2 ] ) pi
( 6a - 4a ) pi
( 2a ) pi
the circumference of a circle.
best wishes,
Sarah
