Question 1016136
slope equation {{{m=(y2-y1)/(x2-x1)}}}

This is introduced for the fact that 2 lines which are perpendicular have slopes that are negative reciprocals of each other. So, we'll calculate the slopes formed by the lines joining these points.

AB -   {{{m=(4-0)/(-1-2)}}}    {{{m=(4)/(-3)}}} 

BC -   {{{m=(-3-4)/(-2--1)}}}    {{{m=(-7)/(-1)}}} {{{m=(7)}}} 

AC -  {{{m=(-3-0)/(-2-2)}}}    {{{m=(-3)/(-4)}}} {{{m=(3)/(4)}}} 

Lines AB and AC have slopes which are negative reciprocals, and they meet at point A.