[mtbopfuyn]

Once you learn the five main rules of rational trigonometry and how to simply apply them, you realise that classical trigonometry represents a misunderstanding of geometry

And yet he's left me still scratching my head since he failed to explain the five main rules.

[Paladin2]

Move to polar/spherical coordinates.

[KC_for_Freedom]

I suspect those rules are "obvious to the casual observer".