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Question

If a is unit vector, then |a×^i|2+|a×^j|2+|a×^k|2= ______

A
3
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B
1
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C
2
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D
0
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Solution

The correct option is C 2
Let a=a1^i+a2^j+a3^k
Then
|a×^i|2=|a1^i+a2^j+a3^k)×i|2 =|a3^ja2^k|2

Similarly, |a×^j|2=|a1^ka3^i|2
|a×^k|2=|a2^ia1^j|2

Therefore, |a×^i|2+|a×^j|2+|a×^k|2=(a23+a22)+(a21+a23)+(a22+a21)=2|a|2=2

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