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Question Number 108638 by bemath last updated on 18/Aug/20
   ((bemath)/★)  prove that  (((n−1)),((     r)) ) +  (((n−1)),((r−1)) ) =  ((n),(r) )
$$\:\:\:\frac{{bemath}}{\bigstar} \\ $$$${prove}\:{that}\:\begin{pmatrix}{{n}−\mathrm{1}}\\{\:\:\:\:\:{r}}\end{pmatrix}\:+\:\begin{pmatrix}{{n}−\mathrm{1}}\\{{r}−\mathrm{1}}\end{pmatrix}\:=\:\begin{pmatrix}{{n}}\\{{r}}\end{pmatrix} \\ $$
Answered by bemath last updated on 18/Aug/20

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