clearly, d = -1/2
use that to find a = -5-9d
Then you want
S20 = 20/2 (2a+19d)
The 10th and 15th terms of an AP are -5 and -7 1/2 respectively find the sum of the first 20 terms
1 answer
1 answer
2 answers
2 answers
3 answers
1 answer