BCECE Engineering BCECE Engineering Solved Paper-2012

  • question_answer
    If a and b are unit vectors and \[|a+b|=1,\] then \[|a-b|\] is equal to

    A) \[\sqrt{2}\]                                        

    B)         1                            

    C)         \[\sqrt{5}\]                                       

    D)         \[\sqrt{3}\]

    Correct Answer: D

    Solution :

    Given, \[|a+b|=1,|a|=|b|=1\] \[\Rightarrow \]\[|a{{|}^{2}}+|{{b}^{2}}|+2|a||b|=1\] \[\Rightarrow \]\[2|a||b|=-1\] Now, \[|a-b{{|}^{2}}=|a{{|}^{2}}+|b{{|}^{2}}-2|a||b|\]                 \[={{1}^{2}}+{{1}^{2}}-(-1)=3\][From Eq. (i)]                 \[\Rightarrow \]               \[|a-b|=\sqrt{3}\]


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