Question 1106906
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The other tutor didn't answer your question.  Or, rather, he interpreted your question in a way I don't think you intended -- thinking that you were plotting a single point instead of a line.<br>
If you are plotting a single point, "y=3" is not enough information; you need an x value also.<br>
But plotting the line "y=3" is something very different.<br>
In the equation "y=3", we are told nothing about x.  That means x can be any number we choose; the only restriction is that y must be 3.<br>
So if you plot a whole bunch of points using different x values, keeping the y value always 3, what does the graph look like?<br>
It is a horizontal line, crossing the y-axis at (0,3).<br>
Most beginning students think of the x value of a point as how far the point is horizontally from the origin, and the y value as how far the point is vertically from the origin.<br>
But in fact the x value tells you how far you are from the y-axis, and the y value tells you how far you are from the x-axis.<br>
So "y=3" tells you that you are 3 units from the x-axis; since it doesn't tell you anything about the x value, you can choose any x value you want.  The resulting graph is a horizontal line.<br>
Similarly, the equation "x=4" would tell you that you  are 4 units to the right of the y-axis, without telling you anything about the y value.  So the graph of x=4 is a vertical line crossing the x-axis at (4,0).