Intermediate Algebra for College Students (7th Edition)

$x=-4,7$ are the excluded values of $x$ from the domain.
As per given question: $f(x)=\dfrac{7}{x^2-3x-28}$ Need to use factorization to solve the quadratic equation . $\dfrac{7}{x^2-3x-28}=0$ or, $\dfrac{7}{x^2-7x+4x-28}=0$ or, $\dfrac{7}{(x+4)(x-7)}=0$ This implies that $x=-4,7$ the denominator will get zero. Hence, $x=-4,7$ are the excluded values of $x$ from the domain.