4(x-1).(x+5) – (x+2). (x+5) – 3(x ^2+x-2)

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1. Bài làm :

   `4(x-1)(x+5)-(x+2)(x+5)-3(x^2+x-2)`

   `=4(x^2+5x-x-5)-(x^2+5x+2x+10)-3x^2-3x+6`

   `=4x^2+20x-4x-20-x^2-5x-2x-10-3x^2-3x+6`

   `=(4x^2-x^2-3x^2)+(20x-4x-5x-2x-3x)+(-20-10+6)`

   `=6x-24`

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2. 4 . (x – 1) . (x + 5) – (x + 2) . (x + 5) – 3 . (x² + x – 2)

   = 4 . (x² + 5x – x – 5) – (x² + 5x + 2x + 10) – 3x² – 3x + 6

   = 4x² + 20x – 4x – 20 – x² – 5x – 2x – 10 – 3x² – 3x + 6

   = (4x² – x² – 3x²) + (20x – 4x – 5x – 2x – 3x) + (-20 – 10 + 6)

   = 6x – 24

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