原式=y(x+2y)(x-2y)/(x+2y)²×(4xy+x²-2xy)/(x-2y)
=y(x+2y)(x-2y)/(x+2y)²×x(x+2y)/(x-2y)
=xy
当x=√2-1,y=√2+1时,
原式=（√2-1）（√2+1）=2-1=1