Restrictions on Domain

$f\left( x \right) =\frac { x-1 }{ x\left( 1-{ x }^{ 2 } \right) }$ The function above is not defined at all x for which $x\left( 1-{ x }^{ 2 } \right)=0 \implies x=0$ or $1-x^2=0\implies x=0,-1,+1$ . Hence for x=-1, 0 and +1 the function is not defined. And the required sum is $-1+0+1=\boxed 0$