argtanhy
argcothy
~ log 1 + y
2
1- Y
~ log Y + 1
2
y-1
§2. Series expansions
393
for -1 < y < 1.
for Iyl > 1.
Clearly there are analogous formulae for the circular functions, but they
involve the complex Cog and, because of this fact, serve mainly as sources of
errors.