约分下列分式(x-y)/(y-x)³(x²-9)/(6-2x)(x²-1)/(x-x

(x-y)/(y-x)³
=-1/(x-y)²
(x²-9)/(6-2x)
=(x+3)(x-3) /[-2(x-3)]= -(x+3)/2
(x²-1)/(x-x²)
=(x+1)(x-1) /[-x(x-1)] =-(x+1)/x