Sum the following series to n terms :

4 + 6 + 9 + 13 + 18 + ………..

Let s=4 + 6 + 9 + 13 + 18 + …………. + n


shifting each term by one,


s=4 + 6 + 9 + 13 + 18 + ……………….. + nth …..(1)


s= 4 + 6 + 9 + 13 + 18 + …………. + (n - 1)th + nth …(2)


by (1) - (2) we get


0 = 4 + (2 + 3 + 4 + 5 + …….nth - (n - 1)th - nth)


Nth = 4 + (2 + 3 + 4 + 5 + …….nth - (n - 1)th)


Nth = 4 + (2 + 3 + 4 + …….r + 1) ………..(3)


Nth = 4 + (summation upto (n - 1)th term)


we know



Substituting the above-given value in (3)




thus


s = 4 + 6 + 9 + 13 + 18 + …………. + nth =


s = 4 + 6 + 9 + 13 + 18 + …………. + nth =


We know by property that:


∑axn + bxn - 1 + cxn - 2…….d0=a∑xn + b∑xn - 1 + c∑xn - 2…….. + d0∑1


(4)


We know





Thus substituting the above values in(4)






7