Question

the property allows an equation in one variable to be written as a system of equations. done

Explanation:

The equality property (specifically, recognizing that a single-variable equation like $f(x)=g(x)$ can be split into the system

$$\begin{cases} y=f(x) \\ y=g(x) \end{cases}$$

) allows rewriting one-variable equations as a system of equations by setting each side equal to a common variable.

Answer:

Equality