Question 31141
<pre><b><font size = 4>Find the real number for which each rational expression is 
undefined.

    5x+9
 -----------
  4x²-4x-15

A rational expression is undefined if its denominator is 0.

So set the denominator = 0 and solve for x.

 denominator = 4x² - 4x - 15 = 0

The left side factors as

            (2x + 3)(2x - 5) = 0

Use to zero-factor principle.  Set each factor = 0 and solve:

Setting 2x + 3 = 0 gives x = -3/2
Setting 2x - 5 = 0 gives x = 5/2

Therefore the expression is undefined for x = -3/2 or 5/2

Edwin
AnlytcPhil@aol.com</pre>