document.write( "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. \n" ); document.write( "

Algebra.Com's Answer #447186 by stanbon(75887) $\"\"$ $\"About$

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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.
\n" ); document.write( "------------------------
\n" ); document.write( "(4a^2)/[(a-9)(a+9)]
\n" ); document.write( "---
\n" ); document.write( "Undefined if the denominator is zero.
\n" ); document.write( "Undefined if a = 9 or is a = -9
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\n" ); document.write( "Demonstration:
\n" ); document.write( "If a = 9 you get:
\n" ); document.write( "(4*81)/[(0*18)] = 324/0 which is undefined.
\n" ); document.write( "-----
\n" ); document.write( "If a = -9 you get:
\n" ); document.write( "(4*81)/[-18*0] = 324/0 which is undefined.
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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