RAJASTHAN ­ PET Rajasthan PET Solved Paper-2012

  • question_answer
    Two vectors A and B are such that,\[A+B=C\] and\[{{A}^{2}}+{{B}^{2}}={{C}^{2}}\]. If 9 is the angle between positive directions of A and B, then

    A)  \[\theta =\frac{2\pi }{3}\]

    B)  \[\theta =\frac{\pi }{2}\]

    C)  \[\theta =\pi \]

    D)  \[\theta =0\]

    Correct Answer: B

    Solution :

     Given, \[A+B=C\] \[\Rightarrow \]    \[{{C}^{2}}={{A}^{2}}+{{B}^{2}}+2AB\,cos\theta \]       ...(i) But      \[{{C}^{2}}={{A}^{2}}+{{B}^{2}}\] (given)           .... (ii) Comparing Eqs. (i) and (ii), we get \[2AB\text{ }cos\theta =0\] or              \[cos\theta =0\] \[\Rightarrow \] \[\theta =\frac{\pi }{2}\]


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