

Variable X in Algebra
Name: Chris
Status: student
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Question:
Why do we commonly use X for variables in algebra?
Replies:
Hello,
I have read different accounts of why the letter x is used to denote
the unknown in algebraic equations. Renee Descartes might have been
the first to do so, but why? Is it because its easier to write the
letter x, or are there other reasons? Perhaps a brief review of the
history of algebra will lend credence to different explanations.
Algebra has its roots in the Middle East where sciences including
mathematics and astronomy flourished in the Islamic world in the
7001450 period. Muhammad alKhwarizmi (780850) was one of the
major mathematicians of his time and the author of a number of
influential books. One of his major books is on arithmetic and
another on algebra. In fact, it is his transmuted name ‘algorithm’
which we now use to refer to the stepbystep procedures for solving
a problem. His algebra book is titled "Kitab aljabr walmuqabala"
which translates to "the book of calculation by completion and
reduction." The Arabic word "aljabr" is the origin of the word
"algebra" which describes the process of moving terms from one side
of an algebraic equation to the other to find the value of an
unknown. Incidentally, another major figure in the field of algebra
is the famous Omar Khayyam (10481131), a mathematician and poet, who
made significant contributions including describing algebraic
equations whose general solutions were obtained some 400 years later.
In algebraic equations, one solves equations to obtain the value(s)
of one or more unknown(s). The word for "thing" or
"object" (presumably unknown thing or object) in Arabic  which was
the principal language of sciences during the Islamic civilization 
is "shei" which was translated into Green as xei, and shortened to x,
and is considered by some to be the reason for using x. It is also
noteworthy that "xenos" is the Greek word for unknown, stranger,
guest, or foreigner, and that might explain the reasons Europeans
used the letter x to denote the "unknown” in algebraic equations.
Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL
Chris,
Much of algebra developed when feathers dipped in ink were the most common
writing tools. Ballpoint pens, and even pencils, were not yet created.
The two easiest letters to write were x and y. Mathematicians needed
variables they could write quickly without mixing them up. As a result, x
and y are still the two most commonly used variables in algebra.
Convenience produced the tradition.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
Chris,
In truth, we can use any letter we care to use in Algerbra, which is
often convienient for labeling the various factors we try to
calculate. For example, one might say "D=S*T", when we're trying to
say that Distance traveled equals Speed times Time. In higher
levels of math, and in science, there are a number of variable which
are so useful, and always the same value, they are called
constants. These constants often have a specific letter by which
they are commenly identified to make it easy for the people using
these formulas. To keep things from becoming too confusing, with
everyone running around using just any letter for anything, X, Y,
and sometimes Z are used for most problems.
Ryan Belscamper
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Update: June 2012

