Q15 of 167 Page 19

Find the r^thterm of an A.P., the sum of whose first n terms is 3n² +2n

It is given that the sum of n terms is 3n² + 2n

To find: rth term of an AP, the sum of whose first term is 3n² + 2n

So, the sum of n - 1 terms is 3(n - 1)² + 2(n - 1)

formula T_N = S_N - S_{N - 1}

So, T_r = 3r² + 2r - [3(r - 1)² + 2(r - 1)]

T_r = 3r² + 2r - [3(r² + 1 - 2r) + 2(r - 1)]

T_r = - 1 + 6r

Solve:

25 + 22 + 19 + 16 + … + x = 115

Solve:

1 + 4 + 7 + 10 + …. + x = 590

How many terms are there in the A.P. whose first and fifth terms are - 14 and 2 respectively and the sum of the terms is 40?

The sum of the first 7 terms of an A.P. is 10, and that of the next 7 terms is 17. Find the progression

Find the rthterm of an A.P., the sum of whose first n terms is 3n2 +2n