(x-6y)/(x²-4y²)-2y/(2xy-x²)=(x-6y)/((x+2y)(x-2y) - 2y/(x(2y-x))
=(x-6y)/(x+2y)(x-2y) + 2y/(x(x-2y))=
=(x(x-6y) +2y(x+2y))/x(x+2y)(x-2y)=(x²-6xy+2xy+4y²)/(x(x+2y)(x-2y)=
=(x²-4xy+4y²)/x(x+2y)(x-2y)=(x-2y)²/x(x+2y)(x-2y)=
=(x-2y)/x(x+2y)
x≠2y,x≠-2y,x≠0