For nonnegative integers s and r , let s r = s ! r ! s - r !  if  r ≤ s 0  if  r…

For nonnegative integers s and r, let sr=s!r!s-r! if rs0 if r>s. For positive integers m and n, let gm,n=p=0m+nfm,n,pn+pp, where for any nonnegative integer p,
fm,n,p=i=0pmin+ipp+np-i. Then which of the following statements is/are TRUE?
  1. gm, n=gn, m for all positive integers m, n
  2. gm, n+1=gm+1,n for all positive integers m, n
  3. g2m, 2n=2 gm, n for all positive integers m, n
  4. g2m, 2n=gm,n2 for all positive intergers m, n

Solution

fm,n,p=i=0pmin+ipp+np-i

=i=0pCim·n+i!p!n+i-p!·(p+n)!p-i!n+i!

=i=0pCim·(p+n)!p!n!·n!n+i-p!p-i!

=i=0pCim.Cpp+n·Cp-in

Cpp+n·i=0pCim·Cp-in

i=0pCim·Cp-in=Cpm+n

fm,n,p=Cpp+n.Cpm+n

fm,n,pCpp+n=Cpm+n.

gm,n=p=0m+nCpm+n=2m+n

(A) g(2m, 2n)=22m+2n

2gm,n=2.2m+n

(B) gm,n+1=2m+n+1=gm+1,n

(C) g2m,2n=22m+2n=2m+n2=gm,n2

(D) gm,n=gn,m.

Asked in: JEE Advanced 2020 (Paper 2)

Practice more Hyperbola questions on Aicharya