Q18 of 202 Page 10

If the first term of an A.P. is 2 and common difference is 4, then the sum of its 40 terms is

Here a₁= 2

D = common difference = 4

S_n = (2a + (n–1) d)

S₄₀ = (2 x 2 + (39) 4)

= 20 (4 + 156)

= 3,200

In an AP, S_p = q, S_q = p and S_r denotes the sum of first r terms. Then, S_{p + q} is equal to

If S_r denotes the sum of the first r terms of an A.P. Then, S_3n: (S_2n — S_n) is

The number of terms of the A.P. 3, 7, 11, 15, ... to be taken so that the sum is 406 is

Sum of n terms of the series is