The journey to the General Quadratic Formula is a long one. It should begin where there reader is, but I don’t know where that is. As a consequence, I will try to begin a little behind the reader so that I may after a short while catch up with him and then we may journey forward together.
Let us begin with the binomial. A binomial is an expression that has two terms connected by a plus sign, i.e.
Let it be understood now that
and
are stand ins. They might be representing complicated expressions. For example,
is a binomial with
being replaced by $xy$ and
being replaced by
, and
is a binomial with
being replaced by
and
being replaced by
.
Let us now take two such binomials
and
and watch them interact. That is to say I will multiply
by
.
or, to summarize,
We will, for the most part, be concerned with a special case of this in which $A=C=x$. In this case,
or, to summarize,
That quadratic polynomial thing
Now recall the expression
of the first chapter. Since
, I can divide both sides of the equation by it and not change the value of
required for the equation to hold true. That is to say, I can consider
If I am able to find values of
and
so that
and
, then
so that either
and
, that is to say
or
.
There are special cases in which we can, by trial and error, find
and
. Pursuing solutions in this way in an entertaining mental exercise similar to Sudoku, but, for practical purposes, a more general method is required and that general method is the General Quadratic Formula in whose derivation we are currently proceeding.