J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    Find the values of x, y and z from the following equations \[\left[ \begin{matrix}    4 & x-z  \\    2+y & xz  \\ \end{matrix} \right]=\left[ \begin{matrix}    4 & 3  \\    -1 & 10  \\ \end{matrix} \right]\]

    A)  \[x=-5,\text{ }y=3,\text{ }z=2\]

    B)  \[x=5,y=-3,z=2\]

    C)  \[x=5,y=3,\text{ }z=-2\]

    D)  \[x=5,y=-3,z=-2\]

    Correct Answer: B

    Solution :

    Given, \[\left[ \begin{matrix}    4 & x-z  \\    2+y & xz  \\ \end{matrix} \right]=\left[ \begin{matrix}    4 & 3  \\    -1 & 10  \\ \end{matrix} \right]\] On comparing the corresponding elements, we get \[x-z=3\] ?.(i) \[2+y=-1\] \[\Rightarrow \] \[y=-1-2=-3\] ?.(ii) and \[xz=10\] ?.(iii) Now,   \[{{(x+z)}^{2}}={{(x-z)}^{2}}+4xz\] \[={{(3)}^{2}}+4\times 10\] \[=9+40\] \[\Rightarrow \] \[{{(x+z)}^{2}}=49\] \[\Rightarrow \] \[x+z=7\] ?.(iv) On adding Eq. (i) and (iv), we get \[2x=10\] \[\Rightarrow \] \[x=5\] From Eq. (i), we get \[5-z=3\] \[\Rightarrow \] \[-z=3-5\] \[\Rightarrow \] \[z=2\] Hence,  \[x=5,\,y=-3,z=2\]


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