Hello tleave2000I must say, I don't see that either. But the easiest way to solve is as follows:

The general solution of is

(Check out the graph of if you want to confirm this.)

So

Taking the plus sign on the RHS gives , and taking the minus sign gives ; i.e.

So in the range , the solutions are:

Or, in degrees, the solutions you found:

The book's answers are clearly wrong: they just don't give . So, I'm on your side here! I suspect someone has got some wires crossed somewhere.

Grandad