Question Number 141311 by SOMEDAVONG last updated on 17/May/21
$$\mathrm{Show}\:\mathrm{that}\:,\mathrm{C}_{\mathrm{n}} ^{\mathrm{k}} +\mathrm{C}_{\mathrm{n}} ^{\mathrm{k}−\mathrm{1}} =\mathrm{C}_{\mathrm{n}+\mathrm{1}} ^{\mathrm{n}−\mathrm{k}} \\ $$