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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