Bài 3:

3: \(6x\left(x-y\right)-9y^2+9xy\)

\(=6x\left(x-y\right)+9xy-9y^2\)

\(=6x\left(x-y\right)+9y\left(x-y\right)\)

\(=\left(x-y\right)\left(6x+9y\right)\)

\(=3\left(2x+3y\right)\left(x-y\right)\)

Bài 4:

1)a)3(2x-1)(3x-1)-(2x-3)(9x-1)=0

<=>18x²-15x+1-18x²+29x-3=0

<=>14x-2=0

<=>14x=2

<=>x=1/7

b)4(x+1)²+(2x-1)²-8(x-1)(x+1)=11

<=>4x²+8x+4+4x²-4x+1-8x²+8=11

<=>4x+13=11

<=>4x=11-13

<=>4x=-2

<=>x=-1/2

c)Sai đề phải là dấu - chứ không phải +

(x-3)(x²+3x+9)-x(x-2)(x+2)=1

<=>x³-27-x³+4x=1

<=>4x=1+27

<=>4x=28

<=>x=7

2)a)(2x-3y)(2x+3y)-4(x-y)²-8xy

=4x²-9y²-4x²+8xy-4y²-8xy

=-13y²

b)(x-2)³-x(x+1)(x-1)+6x(x-3)

=x³-6x²+12x+8-x³+x+6x²-18x

=8-5x

c)(x-2)(x²-2x+4)(x+2)(x²+2x+4)

=(x-2)(x²+2x+4)(x+2)(x²-2x+4)

=(x³-8)(x³+8)

=x⁶-64

Nguyễn Diệu Thảo sap c hk **** cho  Moon Light

câu 1 a. sai .kết quả =0

1. 3x² - xy+9xy - 3y²

x(3x-y)+3y(3x-y)

(3x-y)(x+3y)

Bài 1: 

a) Ta có: \(\left(15x^2\cdot y^2\cdot z\right):3xyz\)

\(=\dfrac{15x^2y^2z}{3xyz}\)

\(=5xy\)

b) Ta có: \(3x^2\cdot\left(5x^2-4x+3\right)\)

\(=3x^2\cdot5x^2-3x^2\cdot4x+3x^2\cdot3\)

\(=15x^4-12x^3+9x^2\)

c) Ta có: \(\left(2x^2-3x\right):\left(x-4\right)\)

\(=\dfrac{2x^2-8x+5x-20+20}{x-4}\)

\(=\dfrac{2x\left(x-4\right)+5\left(x-4\right)+20}{x-4}\)

\(=2x+5+\dfrac{20}{x-4}\)

d) Ta có: \(-5xy\cdot\left(3x^2y-5xy+y^2\right)\)

\(=-5xy\cdot3x^2y+5xy\cdot5xy-5xy\cdot y^2\)

\(=-15x^3y^2+25x^2y^2-5xy^3\)

Bài làm:

\(\frac{8xy^3\left(x+y\right)}{12x\left(x+y\right)^2}=\frac{2y^3}{3\left(x+y\right)}\)

\(\frac{x^2-xy}{3x^2-3y^2}=\frac{x\left(x-y\right)}{3\left(x-y\right)\left(x+y\right)}=\frac{x}{3\left(x+y\right)}\)