Step-by-step explanation:
the line x = -9 had only one valid x value (-9), but then all values for y between -infinity and +infinity are valid.
does this sound familiar ?
it should, because the y-axis is the same type of line.
it is x = 0.
so, x = -9 is simply parallel to the y-axis.
and any line perpendicular to it (crosses the original line in a right angle = 90 degrees) is then parallel to the x-axis.
there the situation is upside-down: there is only one valid y value, and all values between -infinity and +infinity are valid x values.
since the specified point on that line has y = 1, it means that the whole line is
y = 1
