Vectors 4 Question 7

7. Let the vectors a,b,c and d be such that (a×b)×(c×d)=0. If P1 and P2 are planes determined by the pairs of vectors a,b, and c,d respectively, then the angle between P1 and P2 is

(2000, 2M)

(a) 0

(b) π/4

(c) π/3

(d) π/2

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Answer:

Correct Answer: 7. (a)

Solution:

  1. If θ is the angle between P1 and P2, then normal to the planes are

N1=a×b,N2=c×d

N1×N2=0

Then, |N1|×|N2|sinθ=0

sinθ=0θ=0



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