Example LF.2.1: $m = -2; b = 1: f (x) = -2x + 1$
Draw a mapping diagram yourself or use the diagram created with GeoGebra to explore the diagram further.
Given a point / number, $x$, on the source line, there is a unique
arrow meeting the target line at the point / number, $-2x +
1$, which corresponds to the linear function's value for $x$.
Notice that for each unit increase in $x$ there is a
corresponding decrease by 2 units in the
value of $f(x)$.
Thus there is a constant rate of change for $f$, precisely
$-2$, the value of $m$.