Consider the linear equation $y = 2x - 3$. When plotted on a coordinate plane, its graph forms a straight line. By examining the graph and its accompanying table of values, it is evident that for any given $x$-value (input), there is exactly one corresponding $y$-value (output). Because every element in the domain maps to exactly one value in the range, the relation defined by the equation $y = 2x - 3$ is mathematically a function. Visually, this is confirmed because any vertical dashed line drawn through the graph intersects the line at only a single point, illustrating the core principle of the vertical line test.