The value that makes the rational expression undefined

Find all values for which the rational expression is not defined: 
   
    2x - 7
---------------
x² + 5x - 24

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It is undefined when the denominator is equal to zero.
Find the value of x that makes the denominator equal to zero.

     2x - 7
------------
 x² + 5x - 24

Set the denominator equal to zero and solve for x. 
 
x² + 5x - 24 = 0   {set the denominator equal to 0}
(x + 8)(x - 3) = 0   {factored into two binomials}
x + 8 = 0 or x - 3 = 0   {set each factor equal to 0}
x = -8 or x = 3   {solved for x}

-8 and 3 are the values for x that make the expression undefined.

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