CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2004

  • question_answer
    \[(\vec{a}.\,\hat{i})\,\hat{i}+(\vec{a}\,.\,\hat{j})\,\hat{j}+\,(\vec{a}\,.\,\hat{k})\,\hat{k}\] is equal to :

    A)  \[\vec{a}\]                                        

    B)  \[2\,\vec{a}\]

    C)  \[3\,\vec{a}\]                                  

    D)  \[\vec{0}\]

    Correct Answer: A

    Solution :

    We know that, any vector \[\overrightarrow{a}\] can be uniquely expressed in terms of three non-coplanar vectors as \[\overrightarrow{a}=x\,\hat{i}+y\,\hat{j}+z\,\hat{k}\] multiply scalarly in succession by \[\hat{i},\,\hat{j}\] and \[\hat{k}\], we get \[x=a.\,\,\hat{i},\,y=a.\,\,\hat{j},\,z=a\,.\,\,\hat{k}\] \[\therefore \]                \[\overrightarrow{a}=(a\,.\,\,\hat{i})\,\,\hat{i}+(a\,.\,\,\hat{j})\,\hat{j}+(a\,\,.\,\,\hat{k})\,\,.\,\,\hat{k}\]


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