1. ## arctanh x

Hey ive been asked to find the second deriviative of arctanh x, what on earth is arctanH???? Ive never encountered it before.

thanks

2. Originally Posted by anothernewbie
Thanks, I understand the arctan part, its just the H, are they using this as another variable ie, $\arctan (hx)$?
No, it is the "area hyperbolic tangent" (or inverse hyperbolic tangent) function, the inverse function of the hyperbolic tangent function. Cf. here (and there)

3. Ah super thanks for that i'll have a try and see how i get on with it.