1. The problem statement, all variables and given/known data Solve the following equation by separation of the variables: y' tan-1x - y (1+x2)-1 = 0 2. Relevant equations 3. The attempt at a solution I am not sure if tan-1x stands for arctan x or (tan x)-1. (This has been taken out a book.) Any help on this would be appreciated. If arctan x, then we have to integrate 1 / [(1+x2)(arctan x)] w.r.t x. No idea how to do this. If (tan x)-1, then we have to integrate tan x / (1+x2) w.r.t. x. No idea on how to do this either.