=(x^ 1/2-y^ 1/2)^2/(x-y)

=(x+y-2x^ 1/2y^ 1/2)/(x-y)

=( 12-2*3)/(x-y)

X-y =-[(x-y) 2] 1/2 (the negative sign is taken here because X < y).

=-[(x+y)^2-4xy]^ 1/2

=-( 12^2-4*9)^ 1/2

Root number 3 of =-6

So (x1/2-y1/2)/(x1/2+y1/2)

=- 1/ root number 3