document.write( "Question 431819: Prove nCr = n/(n-r) * n-1Cr using an analytic and combinatoial proof \n" ); document.write( "

Algebra.Com's Answer #299569 by richard1234(7193) $\"\"$ $\"About$

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The right hand side is equal to\r
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\n" ); document.write( "\n" ); document.write( " $\"%28n%2F%28n-r%29%29%28%28n-1%21%29%2F%28n-1-r%29%21r%21%29\"$ \r
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\n" ); document.write( "\n" ); document.write( "Since $\"n%28n-1%29%21+=+n%21\"$ , and $\"%28n-r%29%28n-1-r%29%21+=+%28n-r%29%21\"$ the right hand side is equal to\r
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\n" ); document.write( "\n" ); document.write( " $\"n%21%2F%28n-r%29%21r%21\"$ , same as the left hand side. \n" ); document.write( "

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