Question

The sum of first 8term of an AP is 100 and of first 19term is551 find AP

Answer 1

S8= 8/2[2a+(8-1)d]

100=4(2a+7d)

100=8a+28d. ------1

S19=19/2[2a+(19-1)d]

551=19(a+9d)

551=19a+171d. -------2

now you can solve your question by finding the value of (a) and (d).