Question 142364
find the equation of the line perpendicular to the line x=4 and passing through the point (4,2).
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Since it's perpendicular, it's parallel to the x-axis, or slope = 0.
So, y-y1 = m(x-x1)
y-2 = 0*(x-4)
y-2 = 0
y = 2
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think about it. x=4 is a line 4 units from the y-axis and parallel to it. The eqn, perpendicular to it, has to be parallel to the x-axis. And it goes thru the point (4,2), so y = 2.  It's a line 2 units above the x-axis.