4pi+4tan^-1 x = pi
What about $\displaystyle -\frac{\pi}{2}<\tan^{-1}(x)<\frac{\pi}{2}$ ?
Also, on math help sites, it is common courtesy to not give solutions or further hints after someone has tried to engage the OP to work the problem for themselves. When you do this, you devalue the help trying to be judiciously given.