thu gọn a)x(3x² -2)- x²(3+2) b)2x(3x-2)- 3x(1-x)-9(x² – x+3) c)x²(7-5x) + 5x(x² – 3)- 7(x² +1)

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1. Bạn tham khảo :

   $a,$

   $x(3x^2 – 2) – x^2(3+2)$

   $= 3x^3 – 2x – 3x^2 + 2x^2$ 

   $= 3x^3 – 3x^2 – 2x + 2x^2$

   $= 3x^3 – 3x^2 +2x^3$ 

   $b,$

   $2x(3x-2)- 3x(1-x)-9(x² – x+3)$

   $= 6x – 4x – 3x – 3x^2 – 9x^2  – 9x+3$

   $= -1x – 3x^2 – 9x^2 – 9x+3$   

   $= -1x – 3x^2 + 3 – 9x^2 -9x$

   $= -1x – 3x^3 – 9x^2 – 9x$

   $c,$

   $x²(7-5x) + 5x(x² – 3)- 7(x² +1)$

   $= 7x^2 – 5x^3 + 5x^3  –  15x – 7x^2 – 7$

   $=( 7x^2 – 7x^2) + (-5x^3 + 5x^3) – 15x – 7$

   $= 0 + 0 – 15x – 7$

   $= -15x – 7$

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2. Đáp án:

    

   Giải thích các bước giải:

   $\\\text{a)$x(3x² -2)- x²(3x+2)=x.3x^2-2x-x^2.3x-2x^2=-2x-2x^2$}$

   $\text{b)$2x(3x-2)- 3x(1-x)-9(x² – x+3)$}$

   $\\\text{$=6x^2-4x-3x+3x^2-9x^2+9x-27$}$

   $\text{$=2x-27$}$

   $\\\text{c)$x²(7-5x) + 5x(x² – 3)- 7(x² +1)$}$

   $\text{$=7x^2-5x^3+5x^3-15x-7x^2-7$}$

   $\\\text{$=-15x-7$}$ 

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