Answer
All real numbers except 4 and -10.
Work Step by Step
We know that the function does not exist when the denominator is zero. Thus:
$$ x^2+6x-40=0 \\ \left(x-4\right)\left(x+10\right)=0 \\ x=4,-10$$
Thus, the domain is:
$$ \text{All real numbers except 4 and -10.}$$
