Question 503990
x = 4 is a vertical line.  
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m = slope
m = change in 'y' / change in 'x'
The slope is undefined because there is no change in 'x', which is equivalent to dividing by 0.
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A line perpendicular to a vertical line is a horizontal line.  There is no change in 'y', so its slope is 0.
(It is not undefined. Zero divided by any number from -infinity to +infinity is 0.)
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For a horizontal line to go through the point (3,-2), we simply set y = -2.
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Done.