Why Do α and ω Lack Vector Signs in My Professor's Derivation?

[jumbogala]

Homework Statement

My prof has written out a derivation which says:

\vec{a_{t}} = α x \vec{r}

Why does everything except α have a vector sign on it? I think α should be a vector here too...

By the way, he also derived dv/dt = ω, and v had a vector symbol but ω did not. Is that right or should ω be a vector?

Homework Equations

The Attempt at a Solution

 

[tiny-tim]

Hi jumbogala!

You're right, he's wrong!

(there's probably some psychological reason for it! )

Yes, α and ω are definitely vectors, exactly like a and r.