19 Feb
2016
19 Feb
'16
6:57 p.m.
A neat identity relates inradius r_IN , ex-radius r_EX , altitude h , of a simplex with distinguished base and apex --- *** 1/r_EX + 1/r_IN = 2/h *** --- the altitude equals the harmonic mean of the radii ! I have not come across this elsewhere --- reference, anyone? A fellow by name of Ilya Bogdanov on Math Overflow (carefully rinsing mouth with disinfectant) seems well versed in this stuff. There turn out to be a good few Ilya Bogdanovs in Russia ... does anybody have an email address for this one? WFL