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

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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) About Me  (Show Source):
You can put this solution on YOUR website!
%28r%5E3-9r%29%2F%28r%5E2-9%29
This expression will be undefined when the denominator is zero. So to find the numbers that will make the denominator zero we solve:
r%5E2-9+=+0
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 a%5E2+-+b%5E2+=+%28a%2Bb%29%28a-b%29:
%28r%2B3%29%28r-3%29+=+0
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) About Me  (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 r%5E2-9=0 and solve for 'r' to get r=3 or r=-3


So the expression is undefined when r=3 or r=-3