hello : A partial sum of an arithmetic sequence is : Sn = n/2(U1+Un) U1 = 5 d : the common difference is : 13-9 = 9-5 =4 calculate : n Un = U1 + (n-1)d 441 = 5 +(n-1)(4) 441 = 5 + 4n - 4 4n = 440 n =110 so : 5 + 9 + 13 + . . . + 441 = 110/2(5+441) = 24530
