分式约分a-b/a^2+ab乘a^2b^2-a^4/ab-a^2.
=(a-b)/a(a+b)×a²(b²-a²)/a(b-a)
=a-b;
x^2-3x/x^2-6x+9乘x^2-11x+30/x^2-5.
=x(x-3)/(x-3)²×(x-5)(x-6)/(x²-5)
=x(x-5)(x-6)/(x-3)(x²-5);
16-x^2/x^2-2x-3÷x^2-5x+4/x-3
=(4+x)(4-x)/(x-3)(x+1)×(x-3)/(x-1)(x-4)
=(x+4)/(1-x²);
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