Question

find the sum of the first 15 terms of an arithmetic series 3 + 8 + 11 + 50 and using suitable formula​

Answer 1

Answer:

Sn = n/2[ 2a + (n-1) d]

=> S15 = 15/2[ 2×2 + (15-1) 5]

=> S 15 = 15/2 [ 4 + 90]

=> S 15 = 15/2 × 94

=> S 15 = 15× 47

=> S 15 = 705...