How to eval function I've already created on the eq. writer

[grduran12]

So it's pretty much what the tittle say I create a lot of functions by the DEFINE command and I just want to evaluate them on the equation writer, I've tried typing the name of the function followed by the variables i.e F(1,2,3) but is impossible to write that instead you get something like this F((1,(2,3))), it just don't work, although I'm allowed to copy F(1,2,3) and paste it on the former, so it is possible to evaluate them, but impossible to type it, please help.
I forgot to mention I'm trying this on HP50g