KVPY Sample Paper KVPY Stream-SX Model Paper-2

  • question_answer
    If \[{{\vec{e}}_{1}}\] & \[{{\vec{e}}_{2}}\] are two unit vectors and \[\theta \] is the angle between them, then \[\sin \left( \frac{\theta }{2} \right)\] is:

    A) \[\frac{1}{2}|{{\vec{e}}_{1}}+{{\vec{e}}_{2}}|\]                   

    B) \[\frac{1}{2}|{{\vec{e}}_{1}}+{{\vec{e}}_{2}}|\]

    C) \[\frac{{{{\vec{e}}}_{1}}.{{{\vec{e}}}_{2}}}{2}\]                   

    D) \[\frac{|{{{\vec{e}}}_{1}}\times {{{\vec{e}}}_{2}}|}{2|{{{\vec{e}}}_{1}}||{{{\vec{e}}}_{2}}|}\]

    Correct Answer: B

    Solution :

    \[\text{Consider }\!\!|\!\!\text{ }{{\hat{e}}_{1}}-{{\hat{e}}_{2}}{{|}^{2}}=2-2\cos \theta =4{{\sin }^{2}}\frac{\theta }{2}\] \[\therefore \]      \[\frac{1}{2}|{{\hat{e}}_{1}}-{{\hat{e}}_{2}}|=\sin \frac{\theta }{2}\]


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