This is a link to my Quadratic formula program instructable. You will probably find this instructable helpful too.
Step 1: Getting Started
Step 2: Writing the Program
Look at the pictures below and enter that info on you calculator. To get Prompt, press program, the right arrow, then 2. Then enter A,B,C. make sure that you put the commas in there.
Now hit enter to go to the next line and write (A+B+C)/2->S. This way, you don't even have to find out what the semiperimeter is. To get the arrow symbol, push the STO-> button (right above the ON button).
Step 3: The Equation
If you want to be able know what the answer is before finding the square root of it, then write the same thing again but without the square root. Also, make sure you press STO, Y not X.
Step 4: The Last Bit
Now press comma, open quotes, eleven spaces (alpha, 0) put in the square root symbol, close quotes. Finish it off with ,Y,X. Look at the picture below to see what it should look like.