<image>Given the quadratic function \textit{y}=(\textit{x}-2\textit{a})^{2}+(\textit{a}-1) (\textit{a} is a constant), when \textit{a} takes different values, its graphs form a "family of parabolas". As shown in figure 18, the graphs of the quadratic function are depicted for \textit{a}=-1, \textit{a}=0, \textit{a}=1, and \textit{a}=2. The vertices of these parabolas lie on a straight line, and the equation of this straight line is \textit{y}=____________________.
