初2计算分式题

[(9x^2-1)/(3x^2+x)]*[(x^2-x)/(9x^2-6x+1)]
=[(3x+1)(3x-1)/x*(3x+1)]*[x(x-1)/(3x-1)^2]
=(x-1)/(3x-1)

[(x^2-2x-3)/(x^2-6x+9)]*[(x^2-x)/x(x+1)]
=[(x+1)(x-3)/(x-3)^2]*[x(x-1)/x(x+1)]
=(x-1)/(x-3)

[(x^2-4)/(x^2-4x+4)]÷[(x^2+2x)/(x^2-2x)]
=[(x^2-4)/(x^2-4x+4)]*[(x^2-2x)/(x^2+2x)]
=[(x+2)(x-2)/(x-2)^2]*[x(x-2)/x(x+2)]
=1

[(x^2-4x-5)/(x^2-25)]÷[(x^2+2x+1)/(x^2+5x)]
=[(x^2-4x-5)/(x^2-25)]*[(x^2+5x)/(x^2+2x+1)]
=[(x-5)(x+1)/(x-5)(x+5)]*[(x(x+5)/(x^2+1)^2]
=x/(x+1)

第一题 -72X的平方-6X的三次+X的平方分之487X的三次+81X的平方-X的四次

第二题 3X+9分之2X-3

第三题 题目的-4除x平方-2x分之x平方+2x 不对

第四题 -4x-5除x平方+5x分之x平方+2x+1什么意思看不懂 怎么老是分式上还有一个分式