Thank you, Subhotosh, for taking the time to read
my reply and also for pointing it out to others who don't bother to.
I would just like everyone to know that (unlike someone at the BBC) I
can add, I
do understand reference angles (& ASTC) and, having
taught Maths for nearly thirty years, I'm usually very comfortable with the workings of the Trig Identities.
Unfortunately, my eyesight isn't what it used to be (an age thing), I stay up much too late at night (getting far too tired to operate on all cylinders) and, clearly, I am far too trusting an individual to question the authority of such an esteemed institution as the BBC!
I have reported their error to them but have no response other than an automated email telling me someone (I hope they can add better than the author, lol) will look at my comments; I will check back occasionally to see whether they have fixed it.
Cheers.