Question

find vector v if dot product of vector u and vector v is zero

Answer 1

dot product will be 0 for perpendicular vectos,
there are infinitely many vectors perpendicular to any given vector

like since u.v = 0
say v = <a,b,c>

then 2a-b = 0
so for any values of a,b, and c that satisfy 2a-b=0
the vector v will be perpendicular to u

Answer 2

same thing...