Ncr+nc(r-1)=?

1 Answer
1s2s2p
Jan 29, 2018

#nCr+nC(r-1)=(n![(r-1)!(n-r-1)!+r!(n-r)!])/(r!(n-r)!(n-r-1)!)#

Explanation:

#nCr=(n!)/(r!(n-r)!)#

#nC(r-1)=(n!)/((r-1)!(n-r-1)!)#

#nCr+nC(r-1)=(n!)/(r!(n-r)!)+(n!)/((r-1)!(n-r-1)!)#

#color(white)(nCr+nC(r-1))=(n![(r-1)!(n-r-1)!+r!(n-r)!])/(r!(n-r)!(n-r-1)!)#

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