Question 827745
What is this?   p= -(1,2)
Do you mean this:  p=(-1,-2) ?


Assuming so, slope is vertical change divided by horizontal change.
Let this slope be m.
{{{m=(-2-4)/(-1-2)=3}}}


Let {{{m[o]}}} = the slope for a line perpendicular to the line of slope m.
{{{m*m[o]=-1}}}
{{{3*m[o]=-1}}}
Find {{{m[o]}}}.