SOLUTION: Find all numbers fro which the rational expression is undefined. (r^3-9r)/(r^2-9)

Question 352690: Find all numbers fro which the rational expression is undefined.
(r^3-9r)/(r^2-9)
Found 2 solutions by jsmallt9, jim_thompson5910:
Answer by jsmallt9(3758) (Show Source): You can put this solution on YOUR website!

This expression will be undefined when the denominator is zero. So to find the numbers that will make the denominator zero we solve:

To solve this we factor it (or use the Quadratic Formula). Since this is a difference of squares, this factors very easily according tothe pattern :

From the Zero Product Property we know that this (or any) product is zero only if one (or more) of the factors is zero. So:
r + 3 = 0 or r - 3 = 0
Solving these we get:
r = -3 or r = 3
These are the values for r that will make the denominator zero and, therefore, the expression undefined.
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
The expression is undefined when the denominator is equal to zero. So set the denominator equal to zero to get and solve for 'r' to get or

So the expression is undefined when or
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