Question

in an ap ....Sn=n/2(2a+(n-1)2) ​

Answer 1

Sn is the sum of n terms

first term is a and common difference d

Sn = n/2[a+an].....(1)

we know that

an = a+(n-1)d

put in (1)

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

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

compare it with statement u got d = 2

(2)becomes

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

Sn = n[ a+n-1]