x mũ 3-x mũ 2+8x-4 4x mux2-25-(2x-5)(2x+7) x mũ 3+27+(x+3)(x-9)

x mũ 3-x mũ 2+8x-4
4x mux2-25-(2x-5)(2x+7)
x mũ 3+27+(x+3)(x-9)

0 thoughts on “x mũ 3-x mũ 2+8x-4 4x mux2-25-(2x-5)(2x+7) x mũ 3+27+(x+3)(x-9)”

  1. Giải thích các bước giải:

    Ta có:

    \(\begin{array}{l}
    *)\\
    4{x^2} – 25 – \left( {2x – 5} \right)\left( {2x + 7} \right)\\
     = \left( {4{x^2} – 25} \right) – \left( {2x – 5} \right)\left( {2x + 7} \right)\\
     = \left[ {{{\left( {2x} \right)}^2} – {5^2}} \right] – \left( {2x – 5} \right)\left( {2x + 7} \right)\\
     = \left( {2x – 5} \right)\left( {2x + 5} \right) – \left( {2x – 5} \right)\left( {2x + 7} \right)\\
     = \left( {2x – 5} \right).\left[ {\left( {2x + 5} \right) – \left( {2x + 7} \right)} \right]\\
     = \left( {2x – 5} \right).\left( { – 2} \right)\\
     =  – 2.\left( {2x – 5} \right)\\
    *)\\
    {x^3} + 27 + \left( {x + 3} \right)\left( {x – 9} \right)\\
     = \left( {{x^3} + {3^3}} \right) + \left( {x + 3} \right)\left( {x – 9} \right)\\
     = \left( {x + 3} \right)\left( {{x^2} – 3.x + {3^2}} \right) + \left( {x + 3} \right)\left( {x – 9} \right)\\
     = \left( {x + 3} \right).\left[ {\left( {{x^2} – 3x + 9} \right) + \left( {x – 9} \right)} \right]\\
     = \left( {x + 3} \right).\left( {{x^2} – 2x} \right)\\
     = x.\left( {x + 3} \right)\left( {x – 2} \right)
    \end{array}\)

    Em xem lại đề câu đầu nhé!

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