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

  • question_answer
    If a, b, c are non-zero vectors such that \[\mathbf{a}\,\,.\,\,\mathbf{b}=\mathbf{a}\,\,.\,\,\mathbf{c},\] then which statement is true                                    [RPET 2001]

    A)             b = c

    B)             \[\mathbf{a}\,\bot \,(\mathbf{b}-\mathbf{c})\]

    C)             \[\mathbf{b}=\mathbf{c}\] or \[\mathbf{a}\,\bot \,(\mathbf{b}-\mathbf{c})\]

    D)             None of these

    Correct Answer: C

    Solution :

               \[\mathbf{a}.\mathbf{b}=\mathbf{a}.\mathbf{c}\Rightarrow \mathbf{a}.\mathbf{b}-\mathbf{a}.\mathbf{c}=0\Rightarrow \mathbf{a}.(\mathbf{b}-\mathbf{c})=0\]                                 \[\Rightarrow \]Either \[\mathbf{b}-\mathbf{c}=\mathbf{0}\,\,\text{or}\,\,\mathbf{a}=\mathbf{0}\Rightarrow \mathbf{b}=\mathbf{c}\] or \[\mathbf{a}\bot (\mathbf{b}-\mathbf{c}).\]


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