If →a,→b,→c are vectors of lengths 2,3,4. If →a is orthogonal to →b+→c,→b is orthogonal to →c+→a and →c is orthogonal to →a+→b, then the modulus of →a+→b+→c is
A
√29
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B
√39
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C
√45
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D
2√19
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Solution
The correct option is A√29 ¯¯¯a.(¯¯b+¯¯c)=0 ----(1) ¯¯b.(¯¯c+¯¯¯a)=0 ----(2) ¯¯c.(¯¯¯a+¯¯b)=0 ----(3)
adding (1)+(2)+(3)
we get 2(¯¯¯a.¯¯b+¯¯b.¯¯c+¯¯c.¯¯¯a)=0 So, |¯¯¯a+¯¯b+¯¯c|=√|¯¯¯a|2+|¯¯b|2+|¯¯c|2−2(¯¯¯a⋅¯¯b+¯¯b⋅¯¯c+¯¯c⋅¯¯¯a) =√4+9+16−0 =√29