D is the mid-point of the line segment AB where A is (1, 3) and B is (9, −1). A point has coordinates (, ) where and are variables. (i) Find the coordinates of D. (ii) If 2 = 20, write an equation relating .
(iii) It is given that AC and BC are equal in length.
Find an equation relating and and show that it can be simplified to
= 2 − 9.