a) 20x – 5y e) 4x y – 8xy + 10x y c) x(x + y) – 6x – 6y h) 8x + 12x y – 16x y d) 6x – 9x k) 4xy + 8xyz Bài toán 2 : Phân tích đa thức sau thành nhân tử. a) 3x(x +1) – 5y(x + 1) h) 3x (2y – 3z) – 15x(2y – 3z) b) 3x(x – 6) – 2(x – 6) k) 3x(z + 2) + 5(-x – 2) c) 4y(x – 1) – (1 – x) l) 18x (3 + x) + 3(x + 3) d) (x – 3) + 3 – x m) 14x y – 21xy + 28x y e) 7x(x – y) – (y – x) n) 10x(x – y) – 8y(y – x)

`20x – 5y= 5(4x – y)`

`4xy – 8xy + 10xy= (4 – 8 + 10)xy= 6xy`

`x(x + y) – 6x – 6y= x(x + y – 6) – 6y= (x – 6)(x + y)`

`8x + 12xy – 16xy= 8x + (12 – 16)xy= 8x – 4xy= 4x(2 – y)`

`6x – 9x= (6 – 9)x= –3x`

`4xy + 8xyz= 4xy(1 + 2z)`

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`3x(x + 1) – 5y(x + 1)= (x + 1)(3x – 5y)`

`3x(2y – 3z) – 15x(2y – 3z)= (2y – 3z)(3x – 15x)= –12x(2y – 3z)`

`3x(x – 6) – 2(x – 6)= (x – 6)(3x – 2)`

`3x(z + 2) + 5(–x – 2)= 3x(z + 2) – 5(x + 2)= (z + 2)(3x – 5)`

`4y(x – 1) – (1 – x)= 4y(x – 1) + (x – 1)= (x – 1)(4y + 1)`

`18x(3 + x) + 3(x + 3)= (x + 3)(18x + 3)= 3(x + 3)(6x + 1)`

`(x – 3) + 3 – x= x – 3 + 3 – x= 0`

`7x(x – y) – (y – x)= 7x(x – y) + (x – y)= (x – y)(7x + 1)`

`14xy – 21xy + 28xy= (14 – 21 + 28)xy= 21xy`

`10x(x – y) – 8y(y – x)= 10x(x – y) + 8y(x – y)= (x – y)(10x + 8y)`

`@612009`