Question

Find the direction cosines of $z$-axis.

Answer 1

We know $z$ axis makes an angle ${90}^o$ with the $x$ axis and $y$ axis and makes an angle $0^o$ with $z$ axis itself.

So the dcs of $z$ axis are $(\cos {90}^o,\cos {90}^o,\cos 0^o)=(0,0,1)$.