Let a → = 2 i ^ + j ^ - 2 k ^ and b → = i ^ + j ^ be two vectors. c ¯ is a vector such that…

Let a=2i^+j^-2k^ and b=i^+j^ be two vectors. c¯ is a vector such that a·c=c and c-a=22. If the angle between a×b and c is 30°, then a×b×c is equal to
  1. 32
  2. 23
  3. 2
  4. 32

Solution

Given, a=2i^+j^-2k^

a=4+1+4=3

Now, a×b=i^j^k^21-2110

            =2i^-2j^+k^

Then, a×b=4+4+1=3

Now, we have c-a=22

c-a2=8

c2+a2-2c·a=8

c2+9-2c=8

c2-2c+1=0

c-12=0

c=1

Now, a×b×c=a×bcsin30°

                          =3×1×12=32

 

Asked in: AP EAMCET 2018 (25 Apr Shift 1)

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