How do you program quadratic formula on the TI-86?

You don't have to program it in. Try pressing the 2nd button followed by poly (which is the PRGM key). After that the calc. should say: (POLY order=) After seeing this press the number 2 and then ENTER. The calc. should display a2= a1= a0= and that is where you type in your values pressing enter after each number