If `(r )_(n)` denites the number `r r r"….."`(n digits), where`r=1,2,3,"…….",9` and `a=(6)_(n),b=(8)_(n),c=(4)_(2n),` then

If (r)_n , denotes the number rrr... (n digits) , where r = 1,2,3,...,9 and a=(6)_n,b=(8)_n,c=(4)_(2n) , then

.^(n)C_(r)+2.^(n)C_(r-1)+.^(n)C_(r-2)=

If ""^(n)C _r denotes the numbers of combinations of n things taken r at a time, then the expression ""^(n) C_(r+1) +""^(n)C_(r-1) +2 xx ""^(n)C_r equals

Prove that sum_(r=0)^(2n)(r. ^(2n)C_r)^2=n^(4n)C_(2n) .

Prove that ((n),(r))+2((n),(r-1))+((n),(r-2))=((n+2),(r))

""^(n)C_(r)+2""^(n)C_(r-1)+^(n)C_(r-2) is equal to

If sum_(r=1)^n r^4= a_n then sum_(r=1)^n(2r-1)^4)= (A) a_(2n)+a_n (B) a_(2n)-a_n (C) a_(2n)-16a_n (D) a_(2n)+16b_n

Evaluate (n!)/(r!(n-r)!) , where n=15,r=4

If ^n P_r=960 and ^n C_r=40 ,then, r= a. 3 b. 4 c. 5 d. 6

For ""^(n) C_(r) + 2 ""^(n) C_(r-1) + ""^(n) C_(r-2) =