Question 2226
{{{(c+4)/(c-4)}}}
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To find the domain of a rational expression, you must solve the denominator equal to 0--also known as the vertical asymptote.  <br>
Never, ever, in a 1000 years can a denominator be 0.  This is undefined!!! -4 in the denominator makes it -8 (which is possible and can be included in the domain; however, 4 makes the denominator 0.  4 in the denominator is impossible--no such thing!  Try to put 8/0 in your calculator.  You will get an error message.<br>
Maybe you're looking at the numerator instead.  
-4 + 4 = 0
A 0 in the numerator is perfectly A OK.  If you were to put this in your calculator you would get 0.  0 divided by anything is 0.  This is -4 is included in the domain.
If this doesn't help--PLEASE write back.
Thanks
MS