For the graph of $f$: Find $y=c$ on the Y axis, then find the
point on the graph of $f$ directly right (left) of that point,
$(x_*,c)$, determine it's first coordinate, $x_*$, and that is the
desired value for $x$. |
For the mapping diagram of $f$: Find $y=c$ on the Y axis , then find the focus point of $f$, $F= [m, b]$ on the mapping diagram. Draw the line through F and the point $y=b$, to find the point of intersection of this line with the X axis, $x=x_*$, which is the desired value for $x$. |
Martin Flashman, Oct.21, 2013, Created with GeoGebra