Tentukan S8 dark deret aritmatika berikut. A. 2+8+14+20+... B. 15+12+9+6+...

A.
a = 2
b = 6

Sn = n/2 (2 × a + (n - 1) b)
S8 = 8/2 (2 × 2 + 7 × 6)
S8 = 4 (4 + 42)
S8 = 4 (46)
S8 = 184

B.
a = 15
b = -3

Sn = n/2 (2 × a + (n - 1) b)
S8 = 8/2 (2 × 15 + 7 × (-3))
S8 = 4 (30 + (-21)
S8 = 4 (9)
S8 = 36

ini jawabannya............