Question

Hitunglah jumlah setiap deret aritmetika!
1. (-8) + (-5) + (-2) + .. (sampai 9suku)
beserta cara?

Answer 1

Sn=1/2 nx(2a+(n-1)b)
b= 3
a=-8
sn=1/2(9)x(2(-8)+(9-1)3)
sn=1/2(9)x(-16+8x3)
sn= 1/2(9)x(-16+24)
sn=1/2(9)x8
sn=9x4
note:1/2 bagi dgn 8
sn=36