firstly
They are not 'reverse' functions. They are INVERSE FUNCTIONS.
say you want inverse cos (0.5)
sometimes written as cosa(0.5) where a stands for arc which is the same as inverse
sometimes written as cos -1(0.5) ----- NOTE: this is totally different from [cos(0.5)] -1
Anyway, to put this in the web 2.0 calculator input
2nd, acos, 0.5 =
Other cals may be inv, cos -1, 0.5
REMEMBER
Your calculator must be set to degrees or to radians - whichever you are working in. This is easy to overlook.
The number must be between -1 and 1 inclusive. Otherwise there can be no answer and you will get an error message.
I hope this helps.
+118652 
