1 tìm x a(x-2)*(x+2)+x=2x+x^2+4 b x^2*(x-3)-x^3=x^2+4 c (x-2)*(x+3)=0 D,(x^n-2x^4)*x^2-x^n-1*(2x^3-3x-1)=0 2 , a=2x^4-61x^3-95x^2-31x+64 vs x=32 b x^5

Question

1 tìm x
a(x-2)*(x+2)+x=2x+x^2+4
b x^2*(x-3)-x^3=x^2+4
c (x-2)*(x+3)=0
D,(x^n-2x^4)*x^2-x^n-1*(2x^3-3x-1)=0
2 , a=2x^4-61x^3-95x^2-31x+64 vs x=32
b x^5-2013 x^4+2015x^3-4023x^2 vs x=2012

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Acacia 4 years 2020-11-02T02:41:06+00:00 1 Answers 81 views 0

Answers ( )

  1. Doris
    0
    2020-11-02T02:42:10+00:00
    Reply

    Giải thích các bước giải:

     B1:

    $\begin{array}{l}
    a)(x – 2)(x + 2) + x = 2x + {x^2} + 4\\
     \Leftrightarrow {x^2} – 4 + x = {x^2} + 2x + 4\\
     \Leftrightarrow x =  – 8\\
    b){x^2}(x – 3) – {x^3} = {x^2} + 4\\
     \Leftrightarrow {x^3} – 3{x^2} – {x^3} = {x^2} + 4\\
     \Leftrightarrow 4{x^2} + 4 = 0\left( {vn,4{x^2} + 4 \ge 4 > 0,\forall x} \right)\\
    c)\left( {x – 2} \right)\left( {x + 3} \right) = 0\\
     \Leftrightarrow \left[ \begin{array}{l}
    x – 2 = 0\\
    x + 3 = 0
    \end{array} \right.\\
     \Leftrightarrow \left[ \begin{array}{l}
    x = 2\\
    x =  – 3
    \end{array} \right.\\
    d)\left( {{x^n} – 2{x^4}} \right){x^2} – {x^{n – 1}}\left( {2{x^3} – 3x – 1} \right) = 0\\
     \Leftrightarrow {x^{n + 2}} – 2{x^6} – 2{x^{n + 2}} + 3{x^n} + {x^{n – 1}} = 0\\
     \Leftrightarrow  – {x^{n + 2}} + 3{x^n} + {x^{n – 1}} – 2{x^6} = 0\\
     \Leftrightarrow {x^6}\left( { – {x^{n – 4}} + 3{x^{n – 6}} + {x^{n – 7}} – 2} \right) = 0\\
     \Leftrightarrow \left[ \begin{array}{l}
    {x^6} = 0\\
     – {x^{n – 4}} + 3{x^{n – 6}} + {x^{n – 7}} – 2 = 0
    \end{array} \right.\\
     \Leftrightarrow x = 0
    \end{array}$

    Câu d xem lại đề bài.

    B2:

    a) Ta có:

    $\begin{array}{l}
    A = 2{x^4} – 61{x^3} – 95{x^2} – 31x + 64\\
     = 2\left( {{x^4} – 32{x^3}} \right) + 3\left( {{x^3} – 32{x^2}} \right) – \left( {{x^2} – 32x} \right) – 63\left( {x – 32} \right) – 1952\\
     = \left( {x – 32} \right)\left( {2{x^3} + 3{x^2} – x – 63} \right) – 1952
    \end{array}$

    Khi $x = 32 \Rightarrow A =  – 1952$

    b) Ta có:

    $\begin{array}{l}
    B = {x^5} – 2013{x^4} + 2015{x^3} – 4032{x^2}\\
     = \left( {{x^5} – 2012{x^4}} \right) – \left( {{x^4} – 2012{x^3}} \right) + 3\left( {{x^3} – 2012{x^2}} \right) + 2004{x^2}\\
     = \left( {x – 2012} \right)\left( {{x^4} – {x^3} + 3{x^2}} \right) + 2004{x^2}
    \end{array}$

    Khi $x = 2012 \Rightarrow B = {2004.2012^2}$

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