(3x-1)(3x+1)(x的平方-x-1) (a-3)(a-4)-2(3a-2)(3a-2) （x-1)(x+2)-(2x-3)(2-x)=3x(x-3)

题目

(3x-1)(3x+1)(x的平方-x-1) (a-3)(a-4)-2(3a-2)(3a-2) （x-1)(x+2)-(2x-3)(2-x)=3x(x-3)
(3a-b)(2a-b)-(a-b)的平方-5(-a)的平方

答案

(3x-1)(3x+1)(x^2-x-1)
=(9x^2-1)(x^2-x-1)
=9x^4-9x^3-10x^2+x+1.
(a-3)(a-4)-2(3a-2)(3a-2)
=a^2-7a+12-2(9a^2-12a+4)
= a^2-7a+12
-18a^2+24a-8
=-17a^2+17a+4.
(3a-b)(2a-b)-(a-b)^2-5(-a)^2
=6a^2-5ab+b^2-(a^2-2ab+b^2)-5a^2
=-3ab.
（x-1)(x+2)-(2x-3)(2-x)=3x(x-3)
x^2+x-2+2x^2-7x+6=3x^2-9x,
3x=-4,
x=-4/3.