Q21 of 74 Page 9

Find the sum to n terms of the A.P. whose kth term is 5k + 1.


Tk = 5k + 1

T1 = 5 × 1 + 1 = 6

T2 = 5 × 2 + 1 = 11

T3 = 5 × 3 + 1 = 16

T4 = 5 × 4 + 1 = 21

Now a = 6, d = 11 – 6 = 5

Thus Sn =

             =

             =

             = =

More from this chapter

All 74 →
19
If the pth term of an A.P is and the qth term is , prove that the sum of the first pq terms must be (pq + 1).

20
If the sum of a certain number of terms of the A.P. 25, 22, 19,….. is 116, find the last term.

22
If the sum of n terms of an A.P is (pn + qn2), where p and q are constants, find the common difference.

23
If the sum of n terms of two arithmetic progressions are in the ratio 5n + 4 : 9n + 6, find the ratio of their 18th terms.