Answers

2016-07-10T09:55:49+08:00
3 .. A1=-16 N=20 D=-4 Sn=n/2 [2a1+(n-1)d] S20=20/2[2(-16)+(20-1)-4] S20=10[-32+(19)-4] S20=10[-32+-76] S20=10[-108] S20=-1080
0