angle θfrom the x-axis. Consequently the
PARAMETRIC
EQUATIONS
of the unit circle are x= cos θand y= sin θ,
with θas the parameter.
unknown (indeterminate, variable) A quantity whose
value is to be determined is called an unknown. In
mathematics, finding the value of an unknown usually
requires solving an equation. For the equation 2x+ 5
= 13, for instance, the variable xis the unknown. Alge-
bra shows that this unknown has value 4.
In ancient times, scholars described unknowns and
the equations relating them in words. Ancient Egyptian
scholars used the word heap for an unknown quantity,
and many other cultures simply used the word thing.
Arab scholar M
UHAMMAD IBN
M–
US
–
AAL
-K
HW
–
ARIZM
–
ı
(ca. 780–850), from whose book title Hisab al-jabr
w’al muq–
abala comes the word algebra, used the word
shai to mean an unknown quantity. When his famous
book was translated into Latin, the words res and
causa (depending on the translator) were used for shai.
German scholars of the Renaissance translated causa as
coss, which the English adopted, calling the study of
equations and unknown quantities “the cossic art.”
This name for algebra was popular for many decades.
It literally means “the art of things.”
unknown 517