If →a,→b,→c are three mutually perpendicular vectors of equal magnitude, then the angle θ which →a+→b+→c makes with any one of three given vectors is given by
A
cos−1(1√3)
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B
cos−1(13)
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C
cos−1(2√3)
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D
Noneofthese
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Solution
The correct option is Acos−1(1√3) It is given that, |→a|=|→b|=|→c|=λ (say) and →a,→b,→c are mutually perpendicular vectors.
Therefore,|→a+→b+→c|=√3λ
Let θ be the angle which →a+→b+→c makes with →a.
Then, cosθ=→a.(→a+→b+→c)|→a||→a+→b+→c|=|→a|2|→a||→a+→b+→c|=λ2λ(√3λ)=1√3∴θ=cos−1(1√3)