Question 328485
Perpendicular to a vertical line is a horizontal line of the form {{{y=b}}}.
Use the point to solve for b.
{{{y=9}}}
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{{{drawing(300,300,-10,10,-10,10,circle(1,9,.3),blue(line(5,20,5,-20)),grid(1),graph(300,300,-10,10,-10,10,9))}}}