Exercise 4.4.5

Orthogonal vectors are $(1,-1,0)$ and $(1,1,-1)$. Orthonormal after dividing by their lengths : $\left(\frac{1}{\sqrt{2}},-\frac{1}{\sqrt{2}},0\right)$ and $\left(\frac{1}{\sqrt{3}},\frac{1}{\sqrt{3}},-\frac{1}{\sqrt{3}}\right)$.