Question 201803: explain why the line x=4 is a veritcal line.
Answer by RAY100(1637)   (Show Source):
You can put this solution on YOUR website! Very good question. MOST people have a great deal of difficulty with vertical and horizontal lines.
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In short, Vertical lines have form,,,x=#
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,,,,,,,,,,,,,Horizontal lines have form,,,,y=#
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Remember general linear equations have form, y = mx +b
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Horizontal lines, reason as follows: m=0, therefore, for any x,,(x*0=0), y=b
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Vertical lines,are not as reasonable. Books say to stay away from y=mx +b for vertical lines. Lets do it this way. For any y, x=#. This is the only form that allows y to vary, and x remain constant,( like 0*y = x+b,,,,but mathematically not)
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If a VERTICAL line is coordinated, it is (y1,x),(y2,x) (y3,x),etc: hence x=#, for all y"s
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If a HORIZONTAL line is coordinated, (y,x1),(y,x2), (y,x3), etc: hence y=# for all x"s
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When it is all done, perhaps the best way to remember is that either y=# or x=#, and pick the one that works.
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