Question 155090
Plot two points with x=4
For example: (4,-2) and (4,3)
Draw a line thru them and you will see you get a vertical line.
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Also if you calculate the slope of the line thru those two points
you get m = (3--2)/(4-4) = 5/0
Such a slope is a vertical line.
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Cheers,
Stan H.