(i) Gradient of AB =
gradient of AD = 6
equation of AD is
(ii) D is intercept of this line with y-axis; i.e. (0, -4)
(iii) Perpendicular bisector of AB also has gradient 6, and passes through the mid-point of AB, i.e. (5, 7). So its equation is
(iv) The line in (iii) meets AC at C, where the equations are simultaneously true; i.e. where
I have to go now. Perhaps someone else can pick this up?