Answer
$$x\ne -3, 1$$
Work Step by Step
The denominator cannot equal zero; none of the quadratics in the denominator can be equal to zero.
$$x+3\ne 0$$
$$x\ne -3$$
$$x-1\ne 0$$
$$x\ne 1$$
$$x^2+2x-3\ne 0$$
$$(x+3)(x-1)\ne 0$$
$$x\ne -3, 1$$