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1)解：(9x-9)/(4-4x)
=-9(1-x)/[4(1-x)]
=-9/4
5)解：(x²-7x+12)/(-x²+9x-20)
=(x-3)(x-4)/[-(x-4)(x-5)]
=(3-x)/(x-5)
6)解：(xy-x-y+1)/(y²-2y+1)
=[x(y-1)-(y-1)]/(y-1)²
=(x-1)(y-1)/(y-1)²
=(x-1)/(y-1)
=-9(1-x)/[4(1-x)]
=-9/4
5)解：(x²-7x+12)/(-x²+9x-20)
=(x-3)(x-4)/[-(x-4)(x-5)]
=(3-x)/(x-5)
6)解：(xy-x-y+1)/(y²-2y+1)
=[x(y-1)-(y-1)]/(y-1)²
=(x-1)(y-1)/(y-1)²
=(x-1)/(y-1)
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