if the A.M. between `pth and qth` terms of an A.P. be equal to the A.M. between `rth and sth` terms of the A.P., then show that `p+q=r+s`

Explanation

Let a be the first term and d be the common difference of the given A.P.


Then `a_p = pth term = a + (p − 1)d;`


` a_q = qth term = a + (q − 1)d;`


` a_r = rth term = a + (r − 1)d;`


...