We know that
<span>A (2, 11) and B (7, 1)
step 1
find the slope of a line AB
the slope m=(y2-y1)/(x2-x1)------> m=</span>(1-11)/(7-2)---> m=-10/5----> m=-2
step 2
find the equation of a line AD
we know that
the segment AB and the segment AD are perpendicular
so
m1*m2=-1
m2=-1/m1-----> m2=1/2
with the slope m2=1/2 and the point A(2,11)
y-y1=m*(x-x1)------> y-11=(1/2)*(x-2)----> y=(1/2)x-1+11
y=(1/2)x+10----> y=0.5x+10
the answer is the equation of a line AD is y=0.5x+10
see the attached figure