He did gloss over it, but odd cos and even sin is obvious as soon as you define signed angles (which and lengths (which he forgot to mention). Sin(t) clearly h

He did gloss over it, but odd cos and even sin is obvious as soon as you define signed angles (which and lengths (which he forgot to mention). Sin(t) clearly has the same sign as t. (That's why it's called "sin" ;-) )