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8·The vector P=ai + aj + 3k and Q = ai-2-kareperpendicular to each other. The positive value ofa is:EAMCET 1998, AIIMS 2002](2) 2(4) zero(3) 1

Answer»

If two vectors are perpendicular , their dot product will be Zero. It's a condition

P= ai + aj+3k Q=ai -2j-k

P.Q= (ai+aj+3k).(ai-2j-k)=0 mulitply their equal components

a^2 -2a -3 =0 Factorisation of a^2-2a -3 is (a+1)(a-3)So, a+1=0. a-3=0 a=-1. a=3In positive value ,Here positive value is 3 So the answer is 3



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