let us say, the numbers are "a" and "b"
their sum is -13
a + b = -13
their product is 40
a * b = 40 \(\bf \begin{cases}
a+b=-13\\
a\cdot b=40\implies b=\frac{40}{a}\\
then\\
------------\\
a+\boxed{b}=-13\implies a+\boxed{\frac{40}{a}}=-13
\end{cases}\)
solve for "a",
what is "b"? well, b = 40/a :)
