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Question

Given a=x^i+y^j+2^k,b=^i^j+^k,c=^i+2^j;(ab)=π2,a.c=4 then

A
[abc]2=|a|
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B
[abc]=|a|
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C
[abc]=0
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D
[abc]=|a|2
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Solution

The correct option is D [abc]=|a|2
Given: a=x^i+y^j+2^k

b=^i^j+^k
c=^i+2^j

Now given that (ab)=π2

So, a.b=0xy+2=0 ____ (i)
a.c=4x+2y=4 ___ (ii)

From equation (i) substitute x=y2 in equation (ii)
y2+2y=4y=2
from equation (i) xy+2=0x2+2=0
x=0
So, a=2^j+2^k

Now,
[abc]=∣ ∣022111120∣ ∣
=0(02)2(01)+2(2+1)
=0+2+6
=8

If we check |a|=22+22=8

So, [abc]=|a|2 option 'D' is correct.

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