Question

If the Sum of n terms is 210 the sum of n-1 terms is 171, and the first term is 3. Find the A.P.​

Answer 1

ANSWER:-

S(n)=210 ,

S(n-1)=171,

a=3

We know that,

a(n)=S(n)-S(n-1)

=210-171

a(n)=39

S(n)=n/2{a+a(n)}

210=n/2{3+39}

210=n/2(42)

210=21n

n=210/21

Therefore n=10

a(n)=a+(n-1)d

39=3+(10-1)d

39=3+9d

9d=36

d=36/9

d=4

Hence the AP is

3,7,11,15,19_ _ _ _