Solution
= Solution
{c}
The relevant <inner products> are
$$
\langle1,x\rangle=\frac{-1+0+1}{3}=0,\qquad
\langle1,1\rangle=1,\qquad\langle x,x\rangle=\frac23.
$$
Hence $1$ and $x$ are <orthogonal vectors>. Dividing by their <norms> gives the <orthonormal basis>
$$
\boxed{f=1,\qquad g=\sqrt{\frac32}\,x}
$$
of their <linear span> $U$.