@Capevaldo
@Ravallo: This question is quite an advanced linear graph question. It's about a year 9-11 question. It involves calculating midpoints, finding the normal/gradient of a graph, finding equations by using formulas etc.
First of all, find the mid point.
(2,3)
Second, find the the gradient of the 2 points using the formula: y1-y2/x1-x2= 4-2/1-3=2/-2=-1
Therefore m= -1.
The bisector must be the normal of the gradient as it is perpendicular.
Normal= -1/m
Therefore the gradient of your bisector is -1/(-1) which is 1.
Use the formula
y2-y1=m(x2-x1)
sub in the midpoint and gradient of the bisector
y-3=1(x-2)
y=x+1
Sorry if I'm wrong, I was in a rush.
If in assistance of any math problems, I can try to assist you in the future.