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Question

Let a=2^i+^j2^k,b=^i+^j. If ^cis a vector such that a.c=|c|,|a+c|=23 and angle between a×b and c is 30, then |(a×b).c|=

A
12
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B
332
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C
3
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D
32
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Solution

The correct option is B 332
Given a=2^i+^j2^k,b=^i+^j
|a|=3,givena.c=|c||a+c|=23|a+c|2=12|a|2+|c|2+2a.c=12
9+|c|2+2|c|=12|c|2+2|c|3=0|c|=1
and |(a×b).c|=|a×b||c|cos30
=|a×b|32=332
[here a×b=∣ ∣ ∣^i^j^k212110∣ ∣ ∣
=^i(2)^j(2)+^k(1)=2^i2^j+^k



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