Question

a parallelogram is drawn with lines joining (x1,y1) and (x2,y2) to the origin as adjacent sides,what are the coordinates of the fourth vertex?

Answer 1

let C (p,q) be fourth vertex
let A(x1,y1) and B (x2,y2) & O(0,0)
mid pt of diagonal AB(x1+x2/2,y1+y2/2)
mid pt of diagonal OC(p/2,q/2)
p=x1+x2,q=y1+y2