I am reading Thé Nature of Magnetism. While reading, I came across a particular approximation of hyperbolic tangent
- while in first case $T>T_c$ , it is just Taylor series,
- in case $T < T_c$ ( where an additional term is added to the argument of the hyperbolic tangent) , the approximation is not clear for me.
Snapshot of Pages
Any hints? Please Thank you very much for your help