If vector ` vecP=a hati + a hatj +3hatk and vecQ=a hati -2 hatj -hatk ` are perpendicular to each other , then the positive value of a is

Explanation

If vectors ` vecP and vecQ ` are perpendicular
`implies vecP . vecQ implies ( a hati + a hat j + 3hatk) .( a hati - 2 hatj - hatk )=0`
` implies a^2 - 2 a -3=0implies a^2 -3a + a -3=0 implies a (a-3) +1 (a -3) =0 implies a=-1,3`