Vectors Help me pls!

Dtermine the value of a so that
u=2i+aj+k and 4i-2j-2k are perpendicular

Did you just start this topic?
This is a very easy question.

if two vectors are perpendicular, then their dot product must be zero

then (2,a,1).(4,-2,-2)=0

8-2a-2=0
a=3

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