Question

the coordinates of the A,B and C of a parallelogram are (210,6) , ( 0,21) and (2,25) respectively .find the coordinates of the fourth vertex D

Answer 1

use parallelogram rule //
we know, mid point of diagonals are concide with one point .

so, midpoint of AC = midpoint of BD
midpoint of AC ={ (210+2)/2, (6+25)/2}

let D =(x , y)

then , midpoint of BD ={(x/2) , (21+y)/2 }

x/2 =212/2
x = 212

(y+21)/2 =(6+25)/2
y =10

so, D=( 212, 10)