Find the value of p for which the vectors vec a = 3i +2j +9k vec b + I + pj +3k are (a) perpendicular (b) parallel

if the vectors a and b are perpendicular.
a.b=0(3i+2j+9k).(i+pj+3k)=03+2p+27=02p+30=02p=-30p=-15
if the vectors are parallel.
31=2p=933p=2p=23

hope this helps you

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