root of a quadratic equation

[tigger]

These two equations help to solve a root of a quadratic equation:
<< 2 ->LIST SWAP / EVAL SWAP -2 / DUP SQ ROT - v/ DUP2 + ROT ROT - >>
<< 3 PICK / SWAP ROT -2 * / DUP SQ ROT - SQRT DUP2 * ROT ROT - >>



[quote='tigger' pid='40913' dateline='1440236517']
<< 2 ->LIST SWAP / EVAL SWAP -2 / DUP SQ ROT - v/ DUP2 + ROT ROT - >>

The calculator put a blank between the - and the 2 automatically. This could have been the mistake in the program.
<< 2 ->LIST SWAP / EVAL SWAP - 2 / DUP SQ ROT - v/ DUP2 + ROT ROT - >>

<< 3 PICK / SWAP ROT -2 * / DUP SQ ROT - SQRT DUP2 * ROT ROT - >>


Is there a sign for SQRT on this page?
When I punched the keys in the calculator itself made a blank between the - and the 2. How could I know that the calculator made this mistake?
Does the HP always makes mistakes like this?
How can I avoid this kind of mistakes?

There might be any hope and help to rectify these short programs?