Chapter 5 - Inner Product Spaces - Review Exercises - Page 284: 12

$$\| v \| =\sqrt{5}.$$ $$\frac{1}{\| v \|}v=\frac{1}{\sqrt{5}}(0,2,-1)$$

Let $ v=(0,2,-1)$, then we have $$\| v \| =\sqrt{\langle v, v\rangle}=\sqrt{v_1^2+v_2^2+v_3^2 }=\sqrt{5}.$$ The unit vector in direction of $v$ is given by $$\frac{1}{\| v \|}v=\frac{1}{\sqrt{5}}(0,2,-1)$$