document.write( "Question 1178378: if f(n)=1/3n(n+1)(n+2), then find f(r)-f(r-1) in simplest form. \n" ); document.write( "

Algebra.Com's Answer #807608 by ikleyn(52781) $\"\"$ $\"About$

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document.write( "For a minute, forget about the factor of  (1/3)  and work with the numerators only\r\n" );
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document.write( "    r*(r+1)*(r+2) - (r-1)*r*(r+1) = r*(r+1) * [ (r+2) - (r-1) ] = 3r*(r+1).\r\n" );
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document.write( "Now recall about this factor (1/3) and get\r\n" );
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document.write( "    f(r) - f(r-1) = r*(r+1)\r\n" );
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document.write( "in the simplest form.\r\n" );
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