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

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

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

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

If ""^(n)C _4 denots 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 ""^(n+2)C_(r+1)

If ""^(n)C _r denots 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 ""^(n+2) C_(r+1)

If ""^(n)C _r denots 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 ""^(n+2) C _(r+1)

If ""(n)C_(r) denotes the number of combinations of n different things taken r at a time, then the vlaue of ""^(n)C_(r+1)+""^(n)C_(r-1) + 2. ""^(n) C_(r) is-