Undefined Algebraic Fractions
Topic Index | Algebra Index | Regents Exam Prep Center

A fraction is said to be undefined
(or have no meaning)
when the denominator = 0.

 

Consider: 

Find a value for x that makes this fraction undefined:

Solution:  determine when the denominator equals 0.
                     
Set the denominator = 0 and solve.

The NUMERATOR IS IGNORED.  It is only necessary to investigate the denominator.

The solution to the above example is:  7 - x = 0,   or    x = 7. 
The fraction is undefined when x = 7.

 

 

Example 1:

Find a value for x that makes this fraction undefined:

To find the answer, solve 5 + x = 0.
The answer is x = -5.
Or simply remember that:  5 + (-5) = 0.

 

Example 2:

Find a value for y that makes this fraction undefined:

To find the answer, solve y2 - 2y - 15 = 0.
(y - 5)(y + 3) = 0
y = 5;  y = -3
The answer is y = 5 or y = -3.