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Question:
If [a×b b×c c×a ]=k [a b c]*2 then what is value of k.here a b &c are vectors?
Answer:

We know that

[a*b  b*c  c*a] = (a*b).[(b*c)*(c*a)]

Now, let d = b*c

So, (b*c)*(c*a) = d*(c*a)

                       = (d.a)c - (d.c)a

                       = {(b*c).a}c - {(b*c).c}a

                       = [b c a]c - [b c c]a

                       = [b c a]c                   {since [b c c] = 0}

                       = [a b c]c                   {since [b c a] = [c a b] = [a b c]} 

Now, (a*b).[(b*c)*(c*a)] = (a*b).{[a b c]c}

                                    = {(a*b).c}[a b c]

                                    = [a b c][a b c]

                                    = [a b c]2

=> [a*b  b*c  c*a] = [a b c]2      ................1

Given, [a*b  b*c  c*a] = k[a b c]2 ...............2

From equation 1 and 2, we get

k = 1

So, the value of k is 1

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