Expert: Sherman D. - 6/16/2004

Question
Hello,
I'd be very thankful if you answer the following two questions:
1-Is there any formula to enable you to calculate the result of a factorial without multiplying by the numbers one by one?(for example what's the result of 7654789!)
2-Is there any formula to enable you to calculate the perimeter of an ellipse having its two diameters?
Thanks a lot for your soon reply  

Answer
1. Sorry i don't think there is a way to make that easier.

2.)
C = Pi{(a + b)(1 + 3x^2/[10 + sqrt(4 - 3x^2)])},
where as x = (a - b)/(a + b)

so this gives you

C = Pi{(a + b)(1 + 3((a - b)/(a + b))^2 / [10 + sqrt(4 - 3((a - b)/(a + b))^2])}

To let you know, "a" and "b" are the radi or diameter/2

info found at http://mathforum.org/dr.math/faq/formulas/faq.ellipse.html