Extraneous Root

extraneous root

[ik¦strān·ē·əs ′rüt]
(mathematics)
A root that is introduced into an equation in the process of solving another equation, but is not a solution of the equation to be solved.

Extraneous Root

 

a root, or solution, of an intermediate equation—an equation obtained in the process of solving a given equation—that is not a root of the given equation. Extraneous roots appear because in solving an equation we cannot always pass to equivalent equations when we simplify it. They may arise, for example, in raising both sides of an equation to a power, in clearing an equation of fractions, or in taking antilogarithms. Thus, the equation log2 (x – 5) + log2 (x – 3) = 3 has the single root x = 7. If, however, we take antilogarithms, we obtain the equation (x – 5)(x – 3) = 8. It has not only the root x = 7 but also the root x= 1, which is an extraneous root of the initial equation.

Mentioned in ?
References in periodicals archive ?
Thus, in this example, squaring both sides of the equation did not introduce an extraneous root.
Extraneous roots are an unsolved mystery for our freshmen level college math students.
Key words: Extraneous roots, Geometry of Extraneous Roots, x Intercepts
Most high school students and college freshmen struggle with the concept of extraneous roots in an algebra course (1).
This is a basic example illustrating how squaring both sides of an equation may introduce extraneous roots.
Thus, geometrically we can see that squaring an equation changes the type of equation it is and thus may introduce extraneous roots.
Note that there is no interest in the extraneous root x = 0.
Unfortunately, extraneous roots are introduced during the algebraic manipulation when an equation is squared to remove the square root present.