- #1
olgerm
Gold Member
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I am trying to understand N-spherical cap area formula (surface area of blue part), but it seems to give wrong answers.
for 1 dimensional cap obviously ## \frac{l_{cap}}{l_{sphere}}=\frac{l_{arc}}{l_{circle}}=\frac{r*θ}{r*2π}=\frac{θ}{2π} ##
But according to wikipedia formula ##\frac{l_{cap}}{l_{sphere}}=\frac{I(\frac{(2r-h)h}{r^2},\frac{n}{2},\frac{1}{2})}{2}##
https://en.wikipedia.org/wiki/Spherical_cap#Hyperspherical_cap
since ##h=r(1-cos(θ))##
## I(a,b,c)=\int_0^a (dx*x^{b-1}*(1-x)^{c-1})## (incomplete beta function)
and ## n=1##
##\frac{l_{cap}}{l_{sphere}}=\int_0^{sin^2(θ)} (\frac{dx}{\sqrt{x-x^2}})/2##
But
##\int_0^{sin^2(θ)} (\frac{dx}{\sqrt{x-x^2}})≠\frac{θ}{2π}##
Where is mistake?
for 1 dimensional cap obviously ## \frac{l_{cap}}{l_{sphere}}=\frac{l_{arc}}{l_{circle}}=\frac{r*θ}{r*2π}=\frac{θ}{2π} ##
But according to wikipedia formula ##\frac{l_{cap}}{l_{sphere}}=\frac{I(\frac{(2r-h)h}{r^2},\frac{n}{2},\frac{1}{2})}{2}##
https://en.wikipedia.org/wiki/Spherical_cap#Hyperspherical_cap
since ##h=r(1-cos(θ))##
## I(a,b,c)=\int_0^a (dx*x^{b-1}*(1-x)^{c-1})## (incomplete beta function)
and ## n=1##
##\frac{l_{cap}}{l_{sphere}}=\int_0^{sin^2(θ)} (\frac{dx}{\sqrt{x-x^2}})/2##
But
##\int_0^{sin^2(θ)} (\frac{dx}{\sqrt{x-x^2}})≠\frac{θ}{2π}##
Where is mistake?