You can put this solution on YOUR website! This actually requires a little thought.
Say you are sitting somewhere on this line.
When you look in the direction of the y-axis,
you always see .
Say you happen to be at , and
then you move over so you see .
You look at the y-axis and still see
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The only line that can allow this is a line
parallel to the x-axis and perpendicular to
the y-axis
Here's the plot:
