Here's a picture of the horizontal line (in green) passing through
the point (9,8)



Look at a bunch of other points on that same horizontal line:



What do all those points have in common besides the fact
that they are all on that same green horizontal line?

Answer:  They all have their SECOND coordinate as 8.

And what letter is used for the SECOND coordinate? x or y?

Answer:  y

So the one equation that describes that green horizontal line and no
other line ia:

      y = 8

That's the equation.  What could be simpler?

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Now here's a picture of the vertical line passing through (9,8)



Look at a bunch of other points on that same vertical line:




What do all those points have in common besides the fact
that they are all on that same green vertical line?

Answer:  They all have their FIRST coordinate as 9.

And what letter is used for the first coordinate? x or y?

Answer:  x

So the one equation that describes that green vertical line and no
other line is:

      x = 9

That's the equation.  What could be simpler?

--------------------------------------------------  

Edwin