History of Hindu Mathematics: A Source Book v2.c17.s8.11

v2.c17.s8.11

The formula for determining the number of terms (n) of an A.P. whose first term (a), common difference (b) and sum (s) are known, is stated in the form $n = (√(8bs + (2a - b)²) - (2a - b))/2b.$