11. Sum of the first p, q and r terms of an A.P. are a, b and c, respectively. Prove that
To prove :
Let and d be the first term and the common difference of AP, respectively.
According to the given information, we have
Subtracting equation (2) from (1), we have
Subtracting equation (3) from (2), we have
Equating values of d, we have
Dividing both sides from pqr, we get
Hence, the given result is proved.