Well, PHP has four 'tan' functions, and in all fairness, I might just remove those functions altogether and leave the basic ones. I do agree that its longer to type now, but at the expense of remembering WTF atan() does.
Well, if you need the atan function you probably know what it should do and apart from that why does the Number:tan method take an array of arguments when only one is ever used? So at least it should be usable like tan(Number::Number::TRIG_ARC).