Question

what is the value of x

Answer 1

A . B = 0 as...A and B are perpendicular

so x = all real numbers ....as x gets multiplied with zero and gets vanished...so x can attain any such value betwee (-infinity , infinity)...or simple x belongs to real number.

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Answer 2

as they are perpendicular

=> (A) (B) = 0

=> (-I+k) (2i+xj+3k) = 0

=> 2(-1) + x(0) +3(1) = 0

=> -2 + 3

=> 1