Question

1,3,5,7,.......sum of first 25odd positive integers is​

Answer 1

a 25 = 1+(25-1)2

a25 = 49

now

Sn=n/2(a+l)

Sn=25/2(50)

Sn= 625

sum of first 25 odd numbers are 625

Answer 2

Answer:

The sum for the n terms of an AP where a is the 1st term, d is the common difference, and l is the last term is given as:

Sn = n/2 [2a + (n-1) d]

a = 1

d = 2

n = 25

= 25/2[2 x 1 + (25-1)2]

= 25/2[2 + 48]

= 25/2[50]

= 25x25

= 625