Haryana PMT Haryana PMT Solved Paper-2010

  • question_answer
    For any two vectors \[\overrightarrow{\text{A}}\]and \[\overrightarrow{\text{B}},\]if \[\overrightarrow{\text{A}}.\]\[\overrightarrow{\text{B}}=\]\[|\overrightarrow{\text{A}}\text{ }\!\!\times\!\!\text{ }\overrightarrow{\text{B}}|,\]is equal to

    A)  \[\sqrt{{{A}^{2}}+{{B}^{2}}}\]                   

    B)  \[A+B\]

    C)  \[\sqrt{{{A}^{2}}+{{B}^{2}}+\frac{AB}{\sqrt{2}}}\]           

    D)  \[\sqrt{{{A}^{2}}+{{B}^{2}}+\sqrt{2}AB}\]

    Correct Answer: D

    Solution :

                    \[AB\,\,\,\cos \theta =AB\,\sin \theta \] \[\Rightarrow \]               \[\tan \theta =1\] \[\Rightarrow \] \[\theta ={{45}^{o}}\] \[\therefore \]  \[|\overrightarrow{c}|=\sqrt{{{A}^{2}}+{{B}^{2}}+2AB\,\,\cos {{45}^{o}}}\]                 \[=\sqrt{{{A}^{2}}+{{B}^{2}}+\sqrt{2}AB}\]


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