Let →u,→v and →w be vectors such that →u+→v+→w=→0. If |→u|=3,|→v|=4 and |→w|=5, then →u.→v+→v.→w+→w.→u is
A
47
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B
-25
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C
0.0
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D
25
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Solution
The correct option is B -25 Since, →u+→v+→w=→0⇒|→u+→v+→w|2=0⇒|→u|2+|→v|2+|→w|2+2(→u.→v+→v.→w+→w.→u)=0⇒9+16+25+2(→u.→v+→v.→w+→w.→u)=0⇒→u.→v+→v.→w+→w.→u=−25