Railways Sample Paper RRB (Assistant Loco Pilot) Sample Test Paper-7

  • question_answer
    For what value of k, will the expression \[3{{x}^{3}}-k{{x}^{2}}+4x+16\]be divisible by \[\left( x-\frac{k}{2} \right)\] ?

    A)  4                                

    B) \[-4\]                

    C)         2                     

    D)         0                    

    Correct Answer: B

    Solution :

    The expression \[3{{x}^{3}}-k{{x}^{2}}+4x+16\]is divisible by \[x-\frac{k}{2}\].              Then, \[x=\frac{k}{2}\] satisfy the equation                               \[\Rightarrow \]   \[3{{\left( \frac{k}{2} \right)}^{3}}-k{{\left( \frac{k}{2} \right)}^{2}}+4\left( \frac{k}{2} \right)+16=0\] \[\Rightarrow \]   \[\frac{3{{k}^{3}}-2{{k}^{3}}+16k+128}{8}=0\] \[\Rightarrow \]   \[{{k}^{3}}+16k+128=0\] \[\Rightarrow \]   \[(k+4)\,({{k}^{2}}-4k+32)=0\] \[\Rightarrow \]    \[k+4=0\] \[\Rightarrow \]   \[k=-4\]


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