I am trying to find the arc cosine of 0.999999999999266
I am getting different answers when using excel, microsoft calculator and this site which gives zero.
i believe the answer (in radians) should be somewhere between 1.2113E-6 and 1.2116E-6 since when I plug back into an equation each of these numbers yields an improper value, straddling the correct derived number for some other function.
