Let a → = i ^ + j ^ + k ^ , b → and c → = j ^ - k ^ be three vectors such that a →…

Let a=i^+j^+k^,b and c=j^-k^ be three vectors such that a×b=c and a·b=1. If the length of projection vector of the vector b on the vector a×c is l, then the value of 3l2 is equal to _____.

Solution

Given,

a×b=c

a×b·c=c2=12+122=2

Here, a×c=i^j^k^11101-1=-2i^+j^+k^

Projection of b on a×c=

b·a×ca×c=

a×b·c22+1+1=

 =262=46

So, 32=2

Asked in: JEE Main 2021 (27 Jul Shift 1)

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