Question 960511
Standard form as a generalized model can be {{{ax+by=c}}}.


If you solve for y in terms of x, you find slope is {{{-a/b}}}.  "Perpendicular to the y axis", means slope is 0.  Using the formula taken from standard form, this means {{{-a/b=0}}}.  This means, {{{highlight_green(a=0)}}}.


You have so far,  {{{by=c}}}.


You want the line to contain the point A (2,1).  The coordinate of x is no longer important;  all possible values of x will be on the horizontal line (given now that slope is 0).  y is 1 everywhere on this line.


{{{b*1=c}}}, but also {{{y=c/b}}} to give the slope-intercept form of the equation.  Obviously this is only a constant, and therefore  c/b is the y-intercept.  You know that the line is {{{highlight(y=1)}}}.  


If you really want as "STANDARD FORM", then adjustment is not needed.  b=1, and c=1.
{{{highlight(0*x+1*y=1)}}}, but this is more formal than necessary.