Factoring X2+1

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    In my high school algebra class I was taught that I could not factor the formula X2+1; that is, that I could not represent it as a product of two formulae as I could with the similar formula

(Eq'n 1)

While factoring a formula does not actually solve an equation, it is nonetheless a part of the puzzle of algebra because it provides us with one of the tools that we use in solving equations. That equation does, in fact, suggest a way to factor x2+1. We need only recall to mind the fact that multiplying two negative numbers together yields a positive number; that is we can represent any positive number as the negative of a negative number, so we have

(Eq'n 2)

in which . Of course that only works if we are allowed to use complex numbers.

    Suppose we restrict our factors to real numbers only. Can we still factor x2+1?

    We know that we cannot devise a pair of real-valued binomials whose product equals x2+1. Could we devise a pair of real-valued trinomials that will work? In that case we would have

(Eq'n 3)

We easily make the identifications A=x and C=1, so we must have

(Eq'n 4)

We solve that readily for and get

(Eq'n 5)

That particular factorization comes in handy in solving the integral .


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