baif2 tìm x a, (x-8).(x^2-2x+9)+(x+1)^3 b, (2x-1)^2-3.(x-1).(x+2)-(x+3)^2

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1. Đáp án:

   $\begin{array}{l}
   a)\left( {x – 8} \right)\left( {{x^2} – 2x + 9} \right) + {\left( {x + 1} \right)^3}\\
    = {x^3} – 2{x^2} + 9x – 8{x^2} + 16x – 72\\
    + {x^3} + 3{x^2} + 3x + 1\\
    = 2{x^3} – 7{x^2} + 28x – 71\\
   b){\left( {2x – 1} \right)^2} – 3\left( {x – 1} \right)\left( {x + 2} \right) – {\left( {x + 3} \right)^2}\\
    = 4{x^2} – 4x + 1 – 3\left( {{x^2} + x – 2} \right) – {x^2} – 6x – 9\\
    = 4{x^2} – 4x + 1 – 3{x^2} – 3x + 6 – {x^2} – 6x – 9\\
    =  – 13x – 2
   \end{array}$

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