Verified answer

((x-y)²+4xy)/((x+y)²-4xy)=(x²-2xy+y²+4xy)/(x²+2xy+y²-4xy)=

=(x²+2xy+y²)/(x²-2xy+y²)=(x+y)²/(x-y)²=(666+333)²/(666-333)²-

=999²/333²=(3*333)²/333²=3²*333²/333²=3²=9.

=(x^2-2xy+y^2-4xy) /(x^2+2xy+y^2-4xy)=(x+y)^2 /(x-y)^2=(666+333)^2 /(666-333)^2=999^2/333^2=(999/333)^2=3^2=9, отв.  9