thu gọn đa thức a. 3x(x-5)-(x-2)7x b. (x+4)(x-4)-2x(3-x) c. (3x-7)(-2x+1)-8x(6-x)

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1. `a) 3x(x – 5) – (x – 2)7x`

   `= 3x. x – 3x. 5 – x. 7x + 2. 7x`

   `= 3x^2 – 15x – 7x^2 + 14x`

   `= (3x^2 – 7x^2) + (-15x + 14x)`

   `= -4x^2 – x`

   `b) (x + 4)(x – 4) – 2x(3 – x)`

   `= x^2 – 4^2 – 2x. 3 + 2x. x`

   `= x^2 – 16 – 6x + 2x^2`

   `= (x^2 + 2x^2) – 6x – 16`

   `= 3x^2 – 6x – 16`

   `c) (3x – 7)(-2x + 1) – 8x(6 – x)`

   `= (3x – 7). -2x + (3x – 7) – 8x. 6 + 8x. x`

   `= 3x. -2x + 7. 2x + 3x – 7 – 48x + 8x^2`

   `= -6x^2 + 14x + 3x – 7 – 48x + 8x^2`

   `= (-6x^2 + 8x^2) + (14x + 3x – 48x) – 7`

   `= 2x^2 – 31x – 7`

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2. `a. 3x(x-5)-(x-2)7x`

   `=3x^2-15x-(7x^2-14x)`

   `=3x^2-15x-7x^2+14x`

   `=-4x^2- x `

   `b. (x+4)(x-4)-2x(3-x)`

   `=x^2-16-6x+2x^2`

   `=3x^2-6x -16`

   `c. (3x-7)(-2x+1)-8x(6-x)`

   `=-6x^2+14x+3x-7-48x+8x^2`

   `=2x^2-31x-7 `

    

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