Question

find the domain of f(x)= 7-x/ x^2-9x

Answer 1

\(\bf f(x)=\cfrac{7-x}{{\color{brown}{ x^2-9x}}}\qquad {\color{brown}{ x^2-9x}}=0\to \cfrac{7-x}{0}\leftarrow undefined\)

thus.... solve the denominator for "0", to see which values for "x" makes it 0, and thus the fraction "undefined"

thus the domain would exclude those values