document.write( "Question 144599: find all numbers for which the rational expression is undefined\r
\n" ); document.write( "\n" ); document.write( "(r^3-3r)/(r^2-81)\r
\n" ); document.write( "\n" ); document.write( "Thank you for your help! \n" ); document.write( "

Algebra.Com's Answer #105330 by vleith(2983) $\"\"$ $\"About$

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The expression is undefined whenever the a value for r results in a denominator with the value $\"0\"$ .\r
\n" ); document.write( "\n" ); document.write( "Set $\"r%5E2-81+=+0\"$ and solve for r.\r
\n" ); document.write( "\n" ); document.write( " $\"r%5E2=81\"$
\n" ); document.write( " $\"r=sqrt%2881%29\"$
\n" ); document.write( " $\"r+=+9\"$ and $\"r=-9\"$ \n" ); document.write( "

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