Because: vector F=( 1,-2,2)
So: vector F- vector b is perpendicular to vector a.
(1-x, -2-x, 2-x) dot product (1, 1) = 0.
So: (1-x)+(-2-x)+(2-x)=0.
So: x= 1/3.
So: vector b=( 1/3, 1/3, 1/3).
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