JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2012

  • question_answer
        The equation of latusrectum of a parabola is \[x+y=8\]and the equation of the tangent at the vertex is\[x+y=12,\]then length of the latusrectum is

    A)  \[4\sqrt{2}\]                     

    B)  \[2\sqrt{2}\]

    C)  8                                            

    D)  \[8\sqrt{2}\]

    Correct Answer: D

    Solution :

                    Since, A is skew symmetric matrix \[\therefore \]  \[{{A}^{T}}=-A\] Now,\[{{({{B}^{T}}AB)}^{T}}={{B}^{T}}{{A}^{T}}{{({{B}^{T}})}^{T}}\](By reversal law)                 \[={{B}^{T}}{{A}^{T}}B\]                                \[[\because {{({{B}^{T}})}^{T}}=B]\]                 \[={{B}^{T}}(-A)B\]                 \[=-{{B}^{T}}AB\]                             \[(\because {{A}^{T}}=-A)\] Hence,\[{{B}^{T}}AB\]is skew symmetric matrix.


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