Answer
all real numbers except $-3$ and $1$.
Work Step by Step
We know that $x^2+2x-3=(x+3)(x-1).$
The denominator cannot be $0$, hence $x+3\ne0$ and $x-1\ne0$, therefore $x\ne-3$ and $x\ne1$.
Thus the domain is all real numbers except $-3$ and $1$.
