Vectors 4 Question 10

10. The vector(s) which is/are coplanar with vectors i^+j^+2k^ and i^+2j^+k^, are perpendicular to the vector i^+j^+k^ is/are

(2011)

(a) j^k^

(b) i^+j^

(c) i^j^

(d) j^+k^

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Answer:

Correct Answer: 10. (a, d)

Solution:

  1. Let a=i^+j^+2k^,b=i^+2j^+k^ and c=i^+j^+k^

A vector coplanar to a and b, and perpendicular to c =λ(a×b)×c=λ(ac)v(bc)a

=λ(1+1+4)(i^+2j^+k^)(1+2+1)(i^+j^+2k^)=λ6i^+12j^+6k^6i^6j^12k^=λ6j^6k^=6λj^k^

For λ=16 Option (a) is correct.

and for λ=16 Option (d) is correct.



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