Question

the 3rd and 8th terms of an arithmetic progression (A.P) are -9 and 26 respectively.find the:a=common difference,b=first term,c=sum of 5th and 7th terms,d=product of 5th and 7th terms.

Answer 1

Using the definitions ....
a+2d = -9
a+7d = 26
subtract them:
5d = 35
d = 7 and a = -23

Now you can find any term in the sequence and should be able to answer
c) and d)