Graphing the equations $y = -3x$ and $y = -3$ on the same rectangular coordinate system clearly demonstrates the differences between linear equations with two variables versus a single variable. For the two-variable equation $y = -3x$, the value of $y$ depends entirely on the chosen value of $x$. Generating a table of values by selecting arbitrary $x$-coordinates yields scattered ordered pairs such as $(0, 0)$, $(1, -3)$, and $(2, -6)$. Plotting these points produces a slanted line that passes through the origin. Conversely, the single-variable equation $y = -3$ lacks an $x$ variable, meaning the $y$-value remains a constant $-3$ regardless of any chosen $x$-coordinate. Creating a table of values for this equation results in ordered pairs like $(0, -3)$, $(1, -3)$, and $(2, -3)$. Plotting these points produces a straight horizontal line that intersects the $y$-axis at $-3$.