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

  • question_answer
    If a and b are adjacent sides of a rhombus, then         [RPET 2001]

    A)             a.b = 0

    B)             a × b = 0

    C)             a.a = b.b

    D)             None of these

    Correct Answer: C

    Solution :

                \[\because \] \[\mathbf{a}\,.\,\mathbf{a}=|\mathbf{a}||\mathbf{a}|\,\,\cos \theta =|\mathbf{a}{{|}^{2}}\],  \[(\because \theta ={{0}^{o}})\]            and  \[\mathbf{b}\,.\,\mathbf{b}=\,|\mathbf{b}||\mathbf{b}|\cos \theta =\,|\mathbf{b}{{|}^{2}}\],  (Here\[\theta ={{0}^{o}}\])            Also, since \[\mathbf{a}\,\text{and}\,\mathbf{b}\] are sides of rhombus                 \ \[|\mathbf{a}|\,=\,|\mathbf{b}|\].  Hence \[\mathbf{a}\,.\,\mathbf{a}=\mathbf{b}\,.\,\mathbf{b}.\]


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