How to find the equation of a vertical line that passes through two points?

First, you need to know what equation form you need to write: point slope, slope-intercept, etc. Considering this case, you need to know the slope, then you must know the y-intercept, and and write like this: ( my example here is for the SLOPE- INTERCEPT form) y=slope times X + y-intercept. 
Hope it helps :D