\left \Vert\matrix{u\cr v\cr w\cr}\right\Vert=\left \Vert\matrix {\frac{-ac}{\sqrt{a^2+b^2}\sqrt{a^2+b^2+c^2}}& \frac{-bc}{\sqrt{a^2+b^2}\sqrt{a^2+b^2+c^2}} & \frac{a^2+b^2}{\sqrt{a^2+b^2}\sqrt{a^2+b^2+c^2}}\cr \frac{b}{\sqrt{a^2+b^2}} & \frac {-a}{\sqrt{a^2+b^2}} & 0\cr 
\frac{a}{\sqtr{a^2+b^2+c^2}}&\frac{b}{\sqtr{a^2+b^2+c^2}}& \frac{c}{\sqtr{a^2+b^2+c^2}}\cr}\right\Vert \left \Vert\matrix{x\cr y\cr z\cr}\right\Vert