Vectors 1 Question 22

23. Let A,B,C be vectors of length 3,4,5 respectively. Let A be perpendicular to B+C,B to C+A and C to A+B. Then, the length of vector A+B+C is … .

(1981, 2M)

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Answer:

Correct Answer: 23. (b)

Solution:

  1. Given, |A|=3,|B|=4,|C|=5

Since, A(B+C)=B(C+A)=C(A+B)=0

|A+B+C|2=|A|+|B|2+|C|2

+2(AB+BC+CA)

=9+16+25+0

[from Eq. (i), AB+BC+CA=0 ]

|A+B+C|2=50|A+B+C|=52



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