Question

A(1,2),B(6,4)C(8,9) are the vertices of the parallelogram ABCD.find the coordinate of D.

Answer 1

let ABCD be the parallelogram
since the diagonal of parallelogram bisect each other
let the coordinates of D be (x,y)
therefore midpoint of AC=Midpoint of BD
(1+8/2,2+9/2)=(6+x/2,4+y/2)
on comparing;
x=3
y=7
D (x,y)=(3,7)