(3y-1)(-9y^2-1)(-1-3y)=

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(3y-1)(-9y^2-1)(-1-3y)=(3y-1)(-9y^2-1)(-1-3y)=(3y-1)(-9y^2-1)(-1-3y)=(3y-1)(-9y^2-1)(-1-3y)=(-1+3y)(

(3y-1)(-9y^2-1)(-1-3y)=
(3y-1)(-9y^2-1)(-1-3y)=

(3y-1)(-9y^2-1)(-1-3y)=
(3y-1)(-9y^2-1)(-1-3y)
=(-1+3y)(-1-3y)(-9y^2-1)
=[(-1)^2-(3y)^2](-9y^2-1)
=(1-9y^2)(-9y^2-1)
=(-9y^2+1)(-9y^2-1)
=(-9y^2)^2-1^2
=81x^4-1

y=kx
x=m/z
则y=km/z
km是常数
所以y是z的反比例函数
(x-2)(x+3)
=x平方+x-6
=ax的平方+bx+c
所以a=1,c=-6
所以a-c=7