Avoid double functions calls

I was thinking that I can take any function and optimize it by storing results already calculated in a temporary variable.
Therefore, I took common mathematical formula, the “quadratic one” that is used to obtain the roots of a polynomial of degree two, and began to prove forms to improve it.

Several were the attempts, and the conclusion at which I arrived is that although he is better to store results of calls of functions, is not the best thing to keep it from operating simpler like the multiplication.

View example