S4=(2a1+3d)/2*4=(2a1+3d)*2
-40=(2a1-9)/2. 2a1-9=-20. 2a1=-11. a1=-5,5
S8=(2a1+7d)/2*8= (-11-21)*4=-128
Copyright © 2025 SCHOLAR.TIPS - All rights reserved.
Answers & Comments
S4=(2a1+3d)/2*4=(2a1+3d)*2
-40=(2a1-9)/2. 2a1-9=-20. 2a1=-11. a1=-5,5
S8=(2a1+7d)/2*8= (-11-21)*4=-128