Question

If the sum of first n terms of an AP is n(n+10),then find the first term and common difference

Answer 1

first term=1(1+10)=11
sum of 1st and 2nd term=2(2+10)=24
2nd term=24-11=13
common difference=13-11=3

Answer 2

first term = s1 = a

n(n+10)=1(1+10)=1(11)=11

so similarly s2 = 24 so

now a2= s2-s1

= 24-11= 13 so

d= 13-11=2