SOLUTION: find all numbers for which the rational expression is undefined (r^3-3r)/(r^2-81) Thank you for your help!

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Question 144599: find all numbers for which the rational expression is undefined
(r^3-3r)/(r^2-81)
Thank you for your help!
Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
The expression is undefined whenever the a value for r results in a denominator with the value 0.
Set r%5E2-81+=+0 and solve for r.
r%5E2=81
r=sqrt%2881%29
r+=+9 and r=-9