化简1.9x-9/4-4x 2.x^2-1/x^2+x-2 3.x^2-4x+4/2x-4 4.3x^2-9x-12/x

1。9x-9/4-4x
=9(x-1)/4(1-x)
=-9/4
2。x^2-1/x^2+x-2
=(x+1)(x-1)/(x-1)(x+2)
=(x+1)/(x+2)
3。x^2-4x+4/2x-4
=(x-2)²/2(x-2)
=(x-2)/2
4。3x^2-9x-12/x^2+2x+1
=3(x-4)(x+1)/(x+1)²
=3(x-4)/(x+1)
5。x^2-7x+12/-x^2+9x-20
=(x-3)(x-4)/-(x-4)(x-5)
=-(x-3)/(x-5)
6。xy-x-y+1/y^2-2y+1
=(y-1)(x-1)/(y-1)²
=(x-1)/(y-1)