Almost everyone knows the Pythagorean theorem—and, is aware also, that E = mc^2 . But everyone who can do simple algebra should also learn how to deduce that E = mc^2 from that Pythagorean theorem—or, rather, from a tiny extension of that famous theorem. That tiny extension is usually called Einstein's Theory of Special Relativity—and this paper shows exactly how that deduction is with ease accomplished, although to do it does require using just a tad more than simple high-school algebra: one small technical mathematical tool contributed by Isaac Newton. In order to get fully on top of relativity, all that is necessary is to copy out this paper (because copying means that each equation is actually absorbed and understood). Copy every bit of it—indeed, it is so important that I recommend that the whole thing be memorized—and to assist you with that, I have provided an appendix, in which every step of the algebra is recapitulated—so no work on your part is involved at all.