SOLUTION: Consider the rational expression: (4a^2) / (a^2-81). What values for a would make this expression undefined? What is the other value for a? Explain and demonstrate why? The answer

Question 731581: Consider the rational expression: (4a^2) / (a^2-81). What values for a would make this expression undefined? What is the other value for a? Explain and demonstrate why? The answer I got was that the expression was undefined because the values for a=9 and 81-81 gives us a denominator of 0. I am lost and I really need help. Thanks.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Consider the rational expression: (4a^2) / (a^2-81). What values for a would make this expression undefined? What is the other value for a? Explain and demonstrate why? The answer I got was that the expression was undefined because the values for a=9 and 81-81 gives us a denominator of 0.
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(4a^2)/[(a-9)(a+9)]
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Undefined if the denominator is zero.
Undefined if a = 9 or is a = -9
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Demonstration:
If a = 9 you get:
(4*81)/[(0*18)] = 324/0 which is undefined.
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If a = -9 you get:
(4*81)/[-18*0] = 324/0 which is undefined.
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Cheers,
Stan H.
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