Let $P$ denote any point $(x, f(x))$ on the graph of a function $f$. Suppose that the line segments $P T$ and $P S$ are perpendicular to the $x$ - and $y$ -axes, respectively. Let $M_{1}, M_{2}$, and $M_{3}$ be, in turn, the midpoints of $P T, P S,$ and $S T$ as shown in FIGURE 1.1.24. Find a function that describes the path of the points $M_{1} .$ Repeat for the midpoints $M_{2}$ and $M_{3}$.