Giúp minh câu 261Cảm ơn

Giúp minh câu 261Cảm ơn

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  1. Đáp án:

    D

    Giải thích các bước giải:

    $$\eqalign{
    & f\left( x \right) = {x^4} + {x^3} – m{x^2} \cr
    & f’\left( x \right) = 4{x^3} + 3{x^2} – 2mx = 0 \cr
    & \Leftrightarrow x\left( {4{x^2} + 3x – 2m} \right) = 0 \cr
    & \Leftrightarrow \left[ \matrix{
    x = 0 \hfill \cr
    4{x^2} + 3x – 2m = 0\,\,\left( 1 \right) \hfill \cr} \right. \cr
    & Ham\,\,so\,\,co\,\,3\,\,cuc\,\,tri \Leftrightarrow \left( 1 \right)\,\,co\,\,2\,\,nghiem\,\,pb\,\,khac\,\,0 \cr
    & \Rightarrow \left\{ \matrix{
    \Delta = {3^2} – 4.4\left( { – 2m} \right) > 0 \hfill \cr
    {4.0^2} + 3.0 – 2m \ne 0 \hfill \cr} \right. \cr
    & \Leftrightarrow \left\{ \matrix{
    9 + 32m > 0 \hfill \cr
    – 2m \ne 0 \hfill \cr} \right. \cr
    & \Leftrightarrow \left\{ \matrix{
    m > – {9 \over {32}} \hfill \cr
    m \ne 0 \hfill \cr} \right. \cr
    & \Rightarrow m \in \left( { – {9 \over {32}}; + \infty } \right)\backslash \left\{ 0 \right\} \cr
    & Chon\,\,D. \cr} $$

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