JEE Main & Advanced Mathematics Vector Algebra Question Bank Scaler or Dot product of two vectors and its application

  • question_answer
    If x and y are two unit vectors and \[\pi \] is the angle between them,  then \[\frac{1}{2}|x-y|\] is equal to               [UPSEAT 2001]

    A)             0

    B)             \[\pi /2\]

    C)             1

    D)             \[\pi /4\]

    Correct Answer: C

    Solution :

               \[|\mathbf{x}-\mathbf{y}{{|}^{2}}=(\mathbf{x}-\mathbf{y})\,.\,(\mathbf{x}-\mathbf{y})=1+1-2|\mathbf{x}||\mathbf{y}|\cos \pi \]                        =\[2-2\,\cos \pi ,\,\,\,\therefore \text{ }|\mathbf{x}-\mathbf{y}|{{\,}^{2}}\,=4\]                                 So, \[\frac{1}{2}|\mathbf{x}-\mathbf{y}|\,=1\],  \[[\because \,\,|\mathbf{x}{{|}^{2}}=\,|\mathbf{y}{{|}^{2}}=1,|\mathbf{x}|\,=\,|\mathbf{y}|=1]\].


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