Those of us who love algebra (and even those who don’t) are familiar with problems that end up with the command to ‘solve for X’. But why, of all the letters in the alphabet, has X been chosen for this singular honor of representing the unknown, a practice that has extended well beyond algebra? To the extent that any of us thought of this at all, we may have put it down to sheer accident. Someone back in time picked that letter for who knows what reason and it stuck as others followed the practice.
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