Um, it depends on exactly what you want to do? In my opinion, this is not the sort of thing that needs an "application". It is too simple a problem.
Often the easiest thing to do if you want a record of your calculation AND a numerical result is to just hit ENTER, then ->NUM. Then the unevaluated expression is in level 2 and the number is in level 1.
Say you're working completely with numbers, though. Then everything will be evaluated as you enter it, right?
Here's a trick around it: Enter the first step as an algebraic object.
Let's say you want to enter sin(1+2*(3-4)^(1/2)).
Hit ' 3-4 Enter. You should have '3.-4.' on the stack. Alternatively, enter 3-4 with the equation writer.
Then you can use RPN normally. The rest of the steps:
2 1/x ^ 2* 1 + sin
you will then have
sin((3.-4.)^(0.5)*2.+1.)
on the stack.
Hit Enter and then EVAL. The equation will be in level 2, the result in level 1.
A couple of caveats: You must be in approx. mode. (Also, for this particular example, complex mode)
Also, sometimes square roots, for whatever reason, trigger an EVAL. That's why we raised to the 0.5 power instead.
