Answer
The set of all real numbers except $1$.
Work Step by Step
The denominator cannot be equal to zero. Solving for the value that makes the denominator zero in the given function, $
f(x)=\dfrac{5x^2}{1-x}
,$ then
\begin{array}{l}\require{cancel}
1-x=0
\\\\
-x=-1
\\\\
x=1
.\end{array}
Hence, the domain is $\text{
the set of all real numbers except $1$
.}$
