If C(n,r)+C(n,r−1)=C(x,y)C(n, r) + C(n, r-1) = C(x, y)C(n,r)+C(n,r−1)=C(x,y), then:
x=n,y=rx=n, y=rx=n,y=r
x=n+1,y=rx=n+1, y=rx=n+1,y=r
x=n+1,y=r+1x=n+1, y=r+1x=n+1,y=r+1
x=n,y=r+1x=n, y=r+1x=n,y=r+1