Railways Sample Paper RRB (Assistant Loco Pilot) Sample Test Paper-2

  • question_answer
    If \[{{\left( 2a-1 \right)}^{2}}+{{\left( 4b-3 \right)}^{2}}+{{\left( 4c+5 \right)}^{2}}=0\] then the value of \[\frac{{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc}{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}\] is

    A)  \[1\frac{3}{8}\]                     

    B)  \[3\frac{3}{8}\]                     

    C)         \[2\frac{3}{8}\]                 

    D)         \[0\]

    Correct Answer: D

    Solution :

    \[{{(2a-1)}^{2}}+{{(4b-3)}^{2}}+{{(4c+5)}^{2}}=0\] \[\begin{matrix}    =2a-1=0;  \\    a=\frac{1}{2};  \\ \end{matrix}\,\,\,\,\,\,\,\,\,\begin{matrix}    4b-3=0;  \\    b=\frac{3}{4};  \\ \end{matrix}\,\,\,\,\,\,\,\,\,\begin{matrix}    4c+5=0  \\    c=\frac{-5}{4}  \\ \end{matrix}\] \[{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc=(a+b+c)({{a}^{2}}+{{b}^{2}}+{{c}^{2}}-ab-bc-ca)\]But    \[a+b+c=0\] So,   \[{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc=0\] So,       \[\frac{{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc}{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}=0\]


You need to login to perform this action.
You will be redirected in 3 sec spinner