Question 153318
Let's look at the formula for the slope of the line,
{{{m=(y[2]-y[1])/(x[2]-x[1])}}}
For the slope to be undefined the denominator must equal 0.
{{{x[2]-x[1]=0}}}
{{{x[2]=x[1]}}}
All x values must be the same.
Given the point, (9,-7), then the
equation is 
{{{x=9}}}
{{{drawing( 300, 300, -10, 10, -10, 10,grid( 1 ),circle(9,-7,.2),
green(line( 9,-10,9,10)))}}}