a)
(x^2+1)(x-3)-(x-3)(x^2+3x+9)
=(x-3)(x^2+1-x^2-3x-9)
=(x-3)(-8-3x)
b)(x+2y)(x^2-2xy+4y^2)-(x-y)(x^2+xy+y^2)
=(x^3+8y^3)-(x^3-y^3)
=x^3+8y^3-x^3+y^3
=8y^3+y^3
c,(2x-3)(2x+3)-(x+5)^2-(x-1)(x+2)
=4x^2-9-x^2+10x +25-x^2-x +2
=2x^2-9x+18
c, 4x^2-4x / xy-y+x-1
=4x(x-1)/(xy-y)+(x-1)
=4x(x-1)/y(x-1)+(x-1)
=4x(x-1)/(x-1)(y+1)
=4x/y+1
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