if the slope of a line is 2/3, then the slope of a parallel line
would be 2/3.
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a vertical line at x=3
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The slope of two lines are perpendicular only if their slopes multiplied together equal -1 (m1*m2 = -1). So if a line has a slope of -3 then a line perpendicular to this one has a slope of -1/-3 or 1/3.