原式=1/(x-3)-6/(x+3)(x-3)-(x-1)/2(x+3)
=[2(x+3)-12-(x-1)(x-3)]/[2(x+3)(x-3)]
=(2x+6-12-x²+4x-3)/[2(x+3)(x-3)]
=-(x²-6x+9)/[2(x+3)(x-3)]
=-(x-3)²/[2(x+3)(x-3)]
=(3-x)/(2x+6)(最简公分母)2(x+3)(x-3)5a-20分之a=5+a^2-9a+20分之5(最简公分母)采纳我，重新问5a-20分之a=5+a^2-9a+20分之5(最简公分母)