-4+(-2)+0+2+.....(hingga 15 suku)

Diket:
a = -4
b = 2-0 = 2

Ditanya : S15?

Jawab:
s15 = 15/2 (2 (-4) + (15-1)2)
s15 = 7,5 (-8 + 14×2)
s15 = 7,5 (-8 + 28)
s15 = 7,5 × 20
s15 = 150

semoga membantu ^__^