Question

The sum of the first 11 terms of an A.p is 19 and the sum of first 19 terms is 11. find the sum of the first 30 terms.

Answer 1

Answer:

Step-by-step explanation

A11=a+10d=19-l

A19=a+18d=11-ll

On elimination

-8d=-8

d=1

Substituting d=1 in l

a=9

Then on putting a and d values in

A30=a+29d =9+29=38