Q28 of 202 Page 9

Find the sum of the first 25 terms of an A.P. whose second and third terms are 14 and 18 respectively.

a₂= 14

a + d = 14 (i)

a₃= 18

a + 2d = 18 (ii)

Subtracting (i) from (ii), we get

d = 4

Putting the value of d in (i), we get

a = 14 – 4 = 10

S₂₅= [2(a) + 24(d)]

= 25 [58]

= 1450

Find the sum of first 25 terms of an A.P. whose n^th term is given by .

Find the sum of the first 25 terms of an A.P. whose n^th term is given by .

If the sum of 7 terms of an A.P. is 49 and that of 17 term is 289, find the sum of n terms.

The first term of an A.P. is 5, the last term is 45 and the sum is 400. Find the number of terms and the common difference.