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If `vec(A)` and `vec(B)` are two non`-`zero vectors such that `|vec(A)+vec(B)|=(|vec(A)-vec(B)|)/(2)` and `|vec(A)|=2|vec(B)|` then the angle between `vec(A)` and `vec(B)` is `:`A. `37^(@)`B. `53^(@)`C. `cos^(-1)(-3//4)`D. `cos^(-1)(-4//3)` |
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Answer» Correct Answer - C `(A^(2)+B^(2)+2AB cos theta)=(1)/(4)(A^(2)+B^(2)-2ABcos theta)` `rArr 3A^(2)+3B^(2)+10ABcos theta=0` or `12B^(2)+3B^(2)+10(2B)(B) cos theta=0` `15B^(2)+20B^(2)cos theta=0` `cos theta=-(3)/(4)` |
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