CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    If a is perpendicular to b, then the vector\[a\times \{a\times \{a\times (a\times b)\}\}\]is equal to

    A)  \[|a{{|}^{2}}b\]              

    B)         \[|a|b\]

    C)  \[|a{{|}^{3}}b\]              

    D)         \[|a{{|}^{4}}b\]

    E)  0

    Correct Answer: D

    Solution :

    Given \[a\bot b\] \[\Rightarrow \] \[a.b=0\] \[=a\times \{a\times \{a\times (a\times b)\}\}\}\] \[=a\times \{a\times \{(a.ba-(a.a)b\}\}\] \[=a\times \{a\times \{0-(a.a)b\}\}\] \[=a\times \{-(a.a)(a\times b)\}\] \[=a\times \{(a.a)(b\times a)\}\] \[=(a.a)\{(a.a)b-(a-b)a\}\] \[=(a.a)\{(a.a)b-0\}\] \[={{(a.a)}^{2}}b\]                           \[(\because (a.a)=|a{{|}^{2}})\] \[={{(|a{{|}^{2}})}^{2}}b\] \[=|a{{|}^{4}}b\]


You need to login to perform this action.
You will be redirected in 3 sec spinner