Hitunglah 2 + 4 + 6 + …. sampai suku ke-8 (Deret geometri)

Jawab:

b = U2 – U1

b = 4 – 2

b = 2

Sn = n/2 . (2a + (n – 1) . b)

S8 = 8/2 . (2 . 2 + (8 – 1) . 2)

S8 = 4 . (4 + 7 . 2)

S8 = 4 . (4 + 14)

S8 = 4 . 18

S8 = 72