• When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
    $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$

  • >>> x = {'a':1, 'b': 2}
    >>> y = {'b':10, 'c': 11}
    >>> z = x.copy()
    >>> z.update(y)
    {'a': 1, 'c': 11, 'b': 10}
    >>> a = {'q':1, 'b': 3}
    >>> b = {'b':2, 'x': r}
    >>> c = x.copy()
    >>> d.update(y)
    {'y': 1, 'q': 11, 'x': 10}