What real values of x are not in the domain of $f(x) = \frac{1}{|x^2 + 3x - 4| + |x^2 + 9x - 10|}$?
Both of those absolute values will be great or equal to zero.
The only time the denominator will be zero is when both absolute expresssions are = 0
so
\(x^2+3x-4 =0\qquad and \qquad x^2+9x-10 = 0\\ (x+4)(x-1)=0 \qquad and \qquad (x+10)(x-1) = 0\\ so \qquad x=1 \)
the only real value of x are not in the domain of f(x) is 1
Here is the graph: