Question 887134
your equation is f(x) = 2x / (x^2 + x - 72)
factor the denominator to get:
f(x) = 2x / ((x+9)*(x-8))
the domain is all real number except x = -9 and x = 8 because either one of those will make the denominator = 0 and that leads to an answer that is undefined.
in set notation, the domain would be described as x is an element of the real number set such that { x element of R | x <> -9, 8 }
R represents the real number set.
here's a tutorial on set notation that might be helpful.
they do a better job of explaining it than i do.
the important point here is that your domain can be all real number except -9 and 8.
<a href = "http://www.purplemath.com/modules/setnotn.htm" target = "_blank">http://www.purplemath.com/modules/setnotn.htm</a>