Given that n∑x=1(x+1)(2x+3) = pn4+qn3+rn2+73n+s, then
i)p=12,q=83 ii)p=13,q=14 iii)r=92,s=0 iv)r=56,s=0
I and III only
Put n = 1, x = 1
Then LHS = (1+1)× (2+3) = 10
RHS = p+q+r+73+s should = 10
Plug in all possible answer values
Options I and III give the right answer as 12+83+92+73=10