ABCD is a square . A≡1,2,B3,−4. If line CD passes through (3,8), then the midpoint of CD is

mAB=−4−23−1=−3Thus, the equation of CD is y−8 =3x−3,i.e., y+3x=17.The equation of the right bisector of AB is y+1=13x−2or 3y=x−5Solving it with line CD, we get x=28/5,  y=1/5. Thus the midpoint of CD is 28/5, 1/5