3n=18 then n=......?

If ""^(n ) C _(3) : ""^(n) C_(2) = 10 : 3 , then n=

If Delta_(r)=|(r-1,n,6),((r-1)^(2),2n^(2),4n-2),((r-1)^(3),3n^(3),3n^(2)-3n)| then sum_(r=1)^(n)Delta_(r)=

If ""^(2n ) C_(3) : ""^(n) C_(2) = 44 : 3 then n=

If a_(n) = (n(n+3))/(n+2) , then find a_(17) .

Electronic transition in He ion takes from n_2 to n_1 shell such that : 2n_2 + 3n_1 = 18 , 2n_2 - 3n_1 = 6 What will be the total number of photons emitted when electrons transit to n_1 shell ?

Lt_(ntooo)[(1)/(3n+1)+(1)/(3n+2)+............+(1)/(3n+n)]=