if its true
then
make
f(x)=(arctan x)(arctan x)
and solve it by parts
remmember that
the derivative of arctan x is 1/(1+x^2)
then i think you should take a subtitution of arctan x=t
because you would have arctan x and its derivative in the same integral
i am not sure its the right way
another way to do by parts is to take 1 as u'
and the rest of the function to take as V
just some thoughts
good luck