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Questions  

If A=2i^+3j^+6k^  andB=3i^6j^+2k^ , then vector perpendicular to both A  and B  has magnitude k times that of(6i^+2j^3k^) . Then k is equal to

a
1
b
4
c
7
d
9

detailed solution

Correct option is C

Let C→  be a vector perpendicular to A→  and B→ Then as per question kC→=A→×B→or   k=(A→×B→)C→          =(2i^+3j^+6k^)×(3i^−6j^+2k^)(6i^+2j^−3k^)         =(42i^+14j^−21k^)(6i^+2j^−3k^)=7∵i^×i^=j^×j^=k^×k^=0 i^×j^=k^     j^×k^=i^   k^×i^=j^

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